U.S. patent number 11,078,333 [Application Number 15/744,398] was granted by the patent office on 2021-08-03 for copolymerization of elemental sulfur to synthesize high sulfur content polymeric materials.
This patent grant is currently assigned to ARIZONA BOARD OF REGENTS ON BEHALF OF THE UNIVERSITY OF ARIZONA. The grantee listed for this patent is ARIZONA BOARD OF REGENTS ON BEHALF OF THE UNIVERSITY OF ARIZONA. Invention is credited to Richard S. Glass, Jared J. Griebel, Soha Namnabat, Robert A. Norwood, Dong-Chul Pyun.
United States Patent |
11,078,333 |
Pyun , et al. |
August 3, 2021 |
Copolymerization of elemental sulfur to synthesize high sulfur
content polymeric materials
Abstract
Copolymerization of elemental sulfur with functional comonomers
afford sulfur copolymers having a high molecular weight and high
sulfur content. Nucleophilic activators initiate sulfur
polymerizations at relative lower temperatures and in solutions,
which enable the use of a wider range of comonomers, such as
vinylics, styrenics, and non-homopolymerizing comonomers.
Nucleophilic activators promote ring-opening reactions to generate
linear polysulfide intermediates that copolymerize with comonomers.
Dynamic sulfur-sulfur bonds enable re-processing or melt processing
of the sulfur polymer. Chalcogenide-based copolymers have a
refractive index of about 1.7-2.6 at a wavelength in a range of
about 5000 nm-8.mu..tau.. The sulfur copolymer can be a
thermoplastic or a thermoset for use in elastomers, resins,
lubricants, coatings, antioxidants, cathode materials for
electrochemical cells, dental adhesives/restorations, and polymeric
articles such as polymeric films and free-standing substrates.
Optical substrates are constructed from the chalcogenide copolymer
and are substantially transparent in the visible and infrared
spectrum.
Inventors: |
Pyun; Dong-Chul (Tucson,
AZ), Glass; Richard S. (Tucson, AZ), Norwood; Robert
A. (Tucson, AZ), Griebel; Jared J. (Tucson, AZ),
Namnabat; Soha (Tucson, AZ) |
Applicant: |
Name |
City |
State |
Country |
Type |
ARIZONA BOARD OF REGENTS ON BEHALF OF THE UNIVERSITY OF
ARIZONA |
Tucson |
AZ |
US |
|
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Assignee: |
ARIZONA BOARD OF REGENTS ON BEHALF
OF THE UNIVERSITY OF ARIZONA (Tucson, AZ)
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Family
ID: |
57757450 |
Appl.
No.: |
15/744,398 |
Filed: |
July 13, 2016 |
PCT
Filed: |
July 13, 2016 |
PCT No.: |
PCT/US2016/042057 |
371(c)(1),(2),(4) Date: |
January 12, 2018 |
PCT
Pub. No.: |
WO2017/011533 |
PCT
Pub. Date: |
January 19, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180208686 A1 |
Jul 26, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62329402 |
Apr 29, 2016 |
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62313010 |
Mar 24, 2016 |
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62306865 |
Mar 11, 2016 |
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62212188 |
Aug 31, 2015 |
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62210170 |
Aug 26, 2015 |
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62203525 |
Aug 11, 2015 |
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62191760 |
Jul 13, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
4/602 (20130101); C08G 75/00 (20130101); C08L
81/04 (20130101); H01M 4/38 (20130101); C08K
3/06 (20130101); C08G 75/16 (20130101); C08F
12/30 (20130101); C08F 212/08 (20130101); H01M
10/052 (20130101); C08G 79/00 (20130101); C08F
12/08 (20130101); C08G 75/14 (20130101); C08L
81/00 (20130101); C08F 12/08 (20130101); C08F
2/38 (20130101); C08F 12/08 (20130101); C08F
2/44 (20130101); C08F 228/02 (20130101); C08F
2/44 (20130101); Y02E 60/10 (20130101); H01M
4/382 (20130101); C08F 228/04 (20130101); C08F
2/38 (20130101); C08F 230/04 (20130101); C08F
228/06 (20130101) |
Current International
Class: |
C08G
75/14 (20060101); C08K 3/06 (20060101); C08F
12/30 (20060101); H01M 4/38 (20060101); C08L
81/00 (20060101); H01M 10/052 (20100101); C08G
75/00 (20060101); C08F 212/08 (20060101); C08F
12/08 (20060101); C08L 81/04 (20060101); C08G
79/00 (20060101); C08G 75/16 (20060101); H01M
4/60 (20060101); C08F 230/04 (20060101); C08F
2/44 (20060101); C08F 228/04 (20060101); C08F
228/06 (20060101); C08F 2/38 (20060101); C08F
228/02 (20060101) |
References Cited
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WO2015123552 |
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Aug 2015 |
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WO |
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|
Primary Examiner: Choi; Ling Siu
Assistant Examiner: Miller; David L
Attorney, Agent or Firm: Nguyen Tarbet LLC
Government Interests
GOVERNMENT SUPPORT
This invention was made with government support under Grant No.
CHE1305773 awarded by NSF. The government has certain rights in the
invention.
Parent Case Text
CROSS REFERENCE
This application claims priority to U.S. Provisional Patent
Application No. 62/191,760 filed Jul. 13, 2015, U.S. Provisional
Patent Application No. 62/203,525 filed Aug. 11, 2015, U.S.
Provisional Patent Application No. 62/210,170 filed Aug. 26, 2015,
U.S. Provisional Patent Application No. 62/212,188 filed Aug. 31,
2015, U.S. Provisional Patent Application No. 62/306,865 filed Mar.
11, 2016, U.S. Provisional Patent Application No. 62/313,010 filed
Mar. 24, 2016, and U.S. Provisional Patent Application No.
62/329,402 filed Apr. 29, 2016, the specification(s) of which
is/are incorporated herein in their entirety by reference.
Claims
What is claimed is:
1. An optical sulfur copolymer comprising: a. sulfur monomers
comprising sulfur chains derived from S.sub.8, at a level of about
50-95 wt % of the optical sulfur copolymer; b. one or more
comonomers each selected from a group consisting of amine monomers,
thiol monomers, sulfide monomers, alkynylly unsaturated monomers,
epoxide monomers, nitrone monomers, aldehyde monomers, ketone
monomers, thiirane monomers, and ethylenically unsaturated monomers
at a level in the range of about 1-49 wt % of the optical sulfur
copolymer; and c. one or more selenium comonomers at a level of
about 1-49 wt % of the optical sulfur copolymer; wherein the one or
more selenium comonomers copolymerize with the sulfur chains
derived from S.sub.8; wherein the optical sulfur copolymer is
transparent in an infrared spectrum.
2. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer has a refractive index of about 1.78-2.6 at a
wavelength in a range of about 500 nm to about 10 .mu.m.
3. The optical sulfur copolymer of claim 1, wherein the one or more
selenium comonomers have the formula Se.sub.nS.sub.(8-n), where n
is an integer that can range from 1-7; or wherein the selenium
comonomers have the formula Se.sub.nS.sub.m, where n is an integer
that can range from 1-7 and m is an integer that can range from
1-7.
4. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is transparent in an electromagnetic spectrum
having a wavelength range of about 1000-1500 nm.
5. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is transparent in an electromagnetic spectrum
having a wavelength range of about 3000-5000 nm.
6. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is transparent in an electromagnetic spectrum
having a wavelength range of about 3-20 microns.
7. The optical sulfur copolymer of claim 1, wherein at least one
functional sulfur moiety of the sulfur monomers is bonded to at
least one functional moiety of the one or more monomers.
8. The optical sulfur copolymer of claim 1, wherein in addition to
the sulfur monomers, the one or more comonomers, and the one or
more selenium monomers, the sulfur copolymer further comprises one
or more epoxide monomers at a level in the range of about 10 wt %
to about 50 wt % of the optical sulfur copolymer.
9. The optical sulfur copolymer of claim 1, wherein in addition to
the sulfur monomers, the one or more comonomers, and the one or
more selenium monomers, the sulfur copolymer further comprises one
or more of a fourth monomer selected from a group consisting of
amine monomers, thiol monomers, sulfide monomers, alkynylly
unsaturated monomers, epoxide monomers, nitrone monomers, aldehyde
monomers, ketone monomers, thiirane monomers, and ethylenically
unsaturated monomers at a level in the range of about 10 wt % to
about 50 wt % of the optical sulfur copolymer.
10. The optical sulfur copolymer of claim 1, wherein in addition to
the sulfur monomers, the one or more comonomers, and the one or
more selenium monomers, the sulfur copolymer further comprises one
or more polyfunctional monomers selected from a group consisting of
a polyvinyl monomer, a polyisopropenyl monomer, a polyacryl
monomer, a polymethacryl monomer, a polyunsaturated hydrocarbon
monomer, a polyepoxide monomer, a polythiirane monomer, a
polyalkynyl monomer, a polydiene monomer, a polybutadiene monomer,
a polyisoprene monomer, a polynorbornene monomer, a polyamine
monomer, a polythiol monomer, a polysulfide monomer, a
polyalkynylly unsaturated monomers, a polynitrone monomers, a
polyaldehyde monomers, a polyketone monomers, and a
polyethylenically unsaturated monomers, wherein the polyfunctional
monomer has moieties that are the same or different.
11. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is processable in a solution.
12. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is melt processable.
13. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is self-healing upon reprocessing.
14. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is formed into a transparent substrate.
15. The optical sulfur copolymer of claim 14, wherein the
transparent substrate is a film, a lens, a window, or a
free-standing object.
16. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is coated on a substrate and cured as a thin
film.
17. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is shaped and cured using a mold.
18. The optical sulfur copolymer of claim 1, wherein the optical
sulfur copolymer is fabricated into an optical device component for
use as a transmitting material in an infrared imaging device.
Description
FIELD OF THE INVENTION
The present invention relates to polymeric compositions and
materials prepared from elemental sulfur. Methods of forming sulfur
copolymers utilize sulfur polymerizations with nucleophilic
activators that can solubilize elemental sulfur, enhance rate of
reactions and widen the scope of accessible comonomers that can
copolymerize with elemental sulfur. The attractive chemical
accessibility and functional diversity of styrenic comonomers and
non-homopolymerizing comonomers are used with elemental sulfur to
prepare a new chemical platform for sulfur-based polymeric
materials and to further enable post-polymerization modifications
for improving the properties of sulfur-based materials.
The present invention further relates to polymeric materials
prepared from sulfur copolymers and chalcogenides having a high
refractive index in the visible and infrared (IR) regime and the
ability to mitigate IR absorbance in the IR optical window.
Furthermore, the polymeric materials of the present invention are
amendable to melt and solution processing to fabricate optical
materials such as lenses, films, and optical fibers, for use in
optical applications such as imaging.
BACKGROUND OF THE INVENTION
An incredible abundance of elemental sulfur, nearly 7-million tons
is generated as a waste byproduct from hydrodesulfurization of
crude petroleum feedstocks, which converts alkanethiols and other
(organo) sulfur compounds into S.sub.8. Before the invention of the
inverse vulcanization process, there were only a limited number of
synthetic methods available to utilize and modify elemental sulfur.
Current industrial utilization of elemental sulfur is centered
around sulfuric acid, agrochemicals, and vulcanization of rubber.
For example, elemental sulfur is used primarily for sulfuric acid
and ammonium phosphate fertilizers, where the rest of the excess
sulfur is stored as megaton-sized, above ground sulfur towers.
While sulfur feedstocks are plentiful, sulfur is difficult to
process. In its original form, elemental sulfur consists of a
cyclic molecule having the chemical formulation S.sub.8. Elemental
sulfur is a brittle, intractable, crystalline solid having poor
solid state mechanical properties, poor solution processing
characteristics, and there is a limited slate of synthetic
methodologies developed for it. Hence, there is a need for the
production of new materials that offers significant environmental
and public health benefits to mitigate the storage of excess sulfur
in powder, or brick form.
Elemental sulfur has been explored for use in lithium-sulfur
electrochemical cells. Sulfur can oxidize lithium when configured
appropriately in an electrochemical cell, and is known to be a very
high energy-density cathode material. The poor electrical and
electrochemical properties of pure elemental sulfur, such as low
cycle stability and poor conductivity) have limited the development
of this technology. For example, one key limitation of
lithium-sulfur technology is the ability to retain high charge
capacity for extended numbers of charge-discharge cycles ("cycle
lifetimes"). Cells based on present lithium ion technology has low
capacity (180 mAh/g) but can be cycled for 500-1000 cycles.
Lithium-sulfur cells based on elemental sulfur have very high
initial charge capacity (in excess of 1200 mAh/g, but their
capacity drops to below 400 mAh/g within the first 100-500 cycles.
Hence, the creation of novel polymer materials from elemental
sulfur feedstocks would be tremendously beneficial in improving
sustainability and energy practices. In particular, improved
battery technology and materials that can extend cycle lifetimes
while retaining reasonable charge capacity will significantly
impact the energy and transportation sectors and further mitigate
US dependence on fossil fuels.
There have been several recent attempts to form sulfur into
nanomaterials for use as cathodes in lithium-sulfur electrochemical
cells, such as impregnation into mesoporous carbon materials,
encapsulation with graphenes, encapsulation into carbon spheres,
and encapsulation into conjugated polymer spheres. While these
examples demonstrate that the encapsulation of elemental sulfur
with a conductive colloidal shell in a core/shell colloid can
enhance electrochemical stability, these synthetic methods are
challenging to implement to larger scale production required for
industrial application. Hence, a new family of inexpensive,
functional materials obtained by practical methods is
desirable.
Reported styrenic polymers consumption in 2013 was estimated to be
about 35,007 kilotons and will grow by 4.81% annually till 2018.
Some key factors driving the styrenic polymer market are increasing
global demand, particularly in Asia, lack of competitive
substitutes that can replace styrenic polymers, and growing use in
various applications. For example, styrenic polymers can be used in
the manufacturing of packaging, consumer goods, tires, pipes and
tanks, marine accessories, wind blades, rotors, ventilators etc.
Moreover, styrenics are inexpensive and are available in a wide
family of functional derivatives for use as reagents in the
chemical and polymer industry. The demand for styrenic polymers
coupled to the overabundance of elemental sulfur can be resolved
with the novel sulfur-styrenic polymers of the present invention.
This new discovery with styrenics can lead to an entirely new
platform of functional sulfur-styrenic polymers with exemplary
applications in improved batteries and tougher plastics.
Conventional, industrially-used vinyl comonomers, such as styrenics
and (meth)acrylics, do not readily copolymerize with sulfur when
conducted in solution copolymerizations and are often insoluble in
liquid sulfur at elevated temperatures. Instead, these comonomers
tend to homopolymerize, particularly when the copolymerization is
conducted in a solution. As used herein, the term "homopolymerize"
is defined as the polymerization of monomer units from the same
monomer. The term "copolymerize" refers to the polymerization of
monomer units of two or more different monomers. While a number of
conventional vinylic comonomers are capable of reacting with sulfur
via free radical processes, either in liquid sulfur or in solution,
the resulting sulfur polymer tends to have a low molar mass, i.e.
less than 2,000 g/mol. Low molecular weight polymers can have
limited functionalities, hence, higher molecular weight polymers
are more desirable. For example, as known to one of ordinary skill
in the art, higher molecular weight polymers can have improved
mechanical properties than that of lower molecular weight polymers.
Therefore, there is a need for high, molecular weight and
functional sulfur polymers derived from the copolymerizations of
sulfur and unsaturated monomers that can copolymerize
free-radically with sulfur, or polymeric sulfur radicals, but
cannot homopolymerize via free radical processes during these
copolymerization reactions.
Previous works have shown that elemental sulfur can be used in its
molten form at elevated temperature (T>120.degree. C.) and
directly used as the reaction medium to react with other comonomers
at elevated temperature (T.apprxeq.120-180.degree. C.). However,
the synthetic chemistry of this process is limited to comonomers
that are soluble in liquid sulfur at elevated temperatures.
Comonomers such as vinylic, styrenic and (meth)acrylic comonomers
that are commonly used in the polymer chemical industry for free
radical polymerizations are typically not miscible with liquid
sulfur, and hence, are not suitable for preparing sulfur
copolymers. For example, since copolymerizations reactions must be
conducted above the melting point of sulfur (T>120.degree. C.),
a large number of important industrial monomers (e.g.
methacrylates, acrylonitrile) are excluded from forming sulfur
copolymers due to their low boiling points (i.e. these comonomers
would boil, or be chemically unstable if heated to T=120.degree.
C.). Previous attempts to conduct copolymerizations of these
commercial comonomers while dissolved in a co-solvent (to
homogenize the medium with sulfur) do not proceed, since dilution
of elemental sulfur greatly reduces the rate of these
polymerizations and suppresses formation of reactive sulfur
radicals.
The present invention features a novel method of forming sulfur
copolymers using nucleophilic activators that promote
polymerization of elemental sulfur with comonomers, in particular,
with challenging comonomers. The methods described herein exploit
the reactivity of reactive intermediates generated by the
nucleophilic ring-opening of elemental sulfur with nucleophiles,
such as amines, to access new polymerization chemistry. The closest
technology is from the known areas of rubber vulcanization for tire
production, where accelerators are used to promote cross-linking of
sulfur with the rubber phase. Elemental sulfur can be solubilized
using nucleophilic activators to form sulfur copolymers by
promoting miscibility and polymerization of elemental sulfur with
comonomers that are of industrial interest, such as styrenics,
methacrylates, acrylates, vinyl ethers, vinyl esters and functional
vinylic comonomers (e.g., acrylonitrile). Moreover, theses
copolymerizations may be conducted with conventional solvents and
at much lower temperatures (T.ltoreq.130.degree. C.). Since current
plastics are solely derived from dwindling fossil fuel feedstocks,
the huge surfeit of elemental sulfur may be used as an alternative
feedstock to prepare a new class of sulfur plastics. Utilization of
these sulfur plastics as electrode components in Li--S batteries
may exhibit significant improved battery performance.
Development of polymeric materials for infrared (IR) optical
applications has not been achieved due to challenges in designing
systems with sufficiently high refractive index (n) and
transparency in the IR spectral regime. To date, organic plastics
exhibit poor performance in the optical window of 1 to 10 .mu.m due
to strong IR absorption from the plastic material. IR optical
technology has numerous potential applications in the civil,
medical, and military areas, where inorganic semiconductors (e.g.,
Ge, Si) and chalcogenide glasses have been widely used as materials
for device components due to their high refractive index
(n.about.2.0-4.0) and low losses from 1-10 .mu.m. Other examples of
glass materials currently in use are InSb, InGaAs, HgCdTe, ArSe,
and ArS. While such materials are well suited for these
applications, they are inherently more expensive, toxic, and
difficult to process in comparison to organic or organic/inorganic
hybrid polymeric materials.
Sulfur has an inherently high refractive index (n is about
1.9-2.0), which is significantly higher than all organic plastic
materials. Moreover, the S--S bonds are largely IR inactive in this
same optical window. Therefore, it is desirable to use elemental
sulfur as the chemical feedstock for these materials was desirable
due to both the low cost of S.sub.8 and favorable optical
properties. However, sulfur is inherently difficult to process into
films and molded objects, and previous synthetic methods have
limited abilities to incorporate sulfur and create polymers with a
high content of S--S bonds. There remains a need to improve the
optical properties of these polymers to enable the development of
these types of materials for mid-IR applications.
Using the inverse vulcanization method, sulfur is enabled to be
prepared into chemically stable polymer plastic materials with
tunable optical and thermochemical properties by simply controlling
the feed ratios of the chemical monomers added to the sulfur
monomers. The resulting sulfur copolymer may be fabricated into
useful optical devices such as films, waveguides, and molded (nano,
micro-) objects and lenses. Currently, chalcogenide glasses are the
primary material of choice for IR optics in the 3-5 micron range
since all organic polymers strongly absorb in the IR optical
regime. The chalcogenide-based copolymers of the present invention
exhibits superior processing advantages over chalcogenide glasses
since the chalcogenide-based copolymer may be solution or melt
processed at relatively lower temperatures.
Chalcogenide-based copolymers can utilize selenium to provide for
the optical properties. The polymerization of liquid S.sub.8 and
elemental selenium (Se.sub.8) to form the chalcogenide copolymer
greatly increases the refractive index of said copolymers. However,
Se.sub.8 is expensive, and can be challenging to work with since it
exhibits different reactivity than S.sub.8 and other comonomers.
Therefore, there is a need for cheaper and simpler solution to
incorporate Se units to form the chalcogenide copolymers. While the
homopolymerization of elemental sulfur or elemental selenium
(Se.sub.8) are known, the polymerization of cyclic selenium
sulfides has not been explored. Using the inverse vulcanization
method, cyclic selenium-sulfides are shown to be a viable comonomer
to prepare chemically stable polymer plastic materials with tunable
optical and thermochemical properties by controlling the feed
ratios of the chemical monomers added. The resulting
chalcogenide-based copolymer may be fabricated into useful optical
devices such as films, waveguides, and molded (nano-, micro-)
objects and lenses.
Any feature or combination of features described herein are
included within the scope of the present invention provided that
the features included in any such combination are not mutually
inconsistent as will be apparent from the context, this
specification, and the knowledge of one of ordinary skill in the
art. Additional advantages and aspects of the present invention are
apparent in the following detailed description and claims.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide for
functional sulfur polymers having a high molecular weight and
sulfur content, and methods of making said sulfur polymers.
Embodiments of the invention are given in the dependent claims.
Embodiments of the present invention can be freely combined with
each other if they are not mutually exclusive.
The copolymerization of elemental sulfur with functional styrenics,
when in liquid sulfur or when dissolved in solution, can afford new
functional sulfur-styrenic polymers carrying side chain groups thru
the styrenic units. New functional groups that can be introduced
into these sulfur-styrenic polymers include halogens (X.dbd.Cl, Br,
F), amines (--NH.sub.2), alkoxy groups (--OCH.sub.3), carboxylic
acids, carboxylate salts, sulfonic acids, sulfonate salts,
quaternary ammonium salts, ethers, oligo-ethers, polyethers,
polyamines, esters, amides, and alcohols.
The presence of one vinyl group, coupled with the unexpected
polymerization mechanism of benzylic proton abstraction from the
polymer backbone can provide a novel approach to prepare
sulfur-styrenic polymers. A wide range of functional
sulfur-styrenic polymer materials can be prepared by direct
copolymerization of a styrenic comonomer with sulfur, or
post-polymerization modification of the sulfur-styrenic polymer
with other monomers (e.g., aniline, epoxides, isocyanates).
In one embodiment, the present invention features a sulfur polymer
comprising about 10-95 wt % of sulfur monomers, and about 5-50 wt %
of non-homopolymerizing monomers. The non-homopolymerizing monomers
can copolymerize with the with the sulfur monomers, via free
radical polymerization, to form the sulfur polymer having a molar
mass of at least 2,000 g/mole.
In another embodiment, the present invention features a sulfur
polymer comprising about 10-95 wt % of sulfur copolymers, and about
5-50 wt % of non-homopolymerizing monomers. The
non-homopolymerizing monomers can copolymerize with the sulfur
copolymers, via free radical polymerization, to form the sulfur
polymer. Preferably, the sulfur polymer has a molar mass of at
least 2,000 g/mole. In some embodiments, the sulfur copolymers
comprises sulfur monomers at about 10-95 wt % of the sulfur
copolymers, and one or more comonomers at about 5-50 wt % of the
sulfur copolymers. The comonomers may be amine comonomers, thiol
comonomers, sulfide comonomers, alkynylly unsaturated comonomers,
epoxide comonomers, nitrone comonomers, aldehyde comonomers, ketone
comonomers, thiirane comonomers, ethylenically unsaturated
comonomers, styrenic comonomers, vinylic comonomers, methacrylate
comonomers, and acrylonitrile comonomer, wherein the one or more
comonomers are copolymerized with the sulfur monomers.
In some embodiments, the non-homopolymerizing monomers are
ethylenically unsaturated monomers, such as maleimide monomers,
norbornene monomers, allylic monomers, monomers having at least one
vinyl ether moiety, and monomers having at least one isopropenyl
moiety.
One of the unique inventive technical features of the present
invention is the use of non-homopolymerizing monomers. Without
wishing to limit the invention to any theory or mechanism, it is
believed that this technical feature of the present invention
advantageously provides for a sulfur polymer having a high
molecular weight, high sulfur content, and improved functionality,
particularly for copolymerizations done in solution (i.e., organic
aromatic solvents). Further, the non-homopolymerizing monomers can
incorporate new functional groups in the sulfur polymer. For
example, inexpensive and commercially available allylic monomers
are monomers that are unable to polymerize with its own monomers,
but can readily copolymerize with sulfur or sulfur copolymer
radicals via free radical polymerizations. The wide range of
functional allylic monomers can provide for functional sulfur
polymers. Other examples of non-homopolymerizing monomers include,
but are not limited to, isopropenyls, maleimides, norbornenes,
vinyl ethers, and methacrylonitriles.
Novel chemical synthetic processes to dramatically expand the scope
of functional comonomers and copolymers that can be prepared to
convert elemental sulfur (S.sub.8) into polymeric materials are
described herein. Previous synthetic systems required synthetic
methods to be conducted in liquid sulfur and at very high
temperatures (T.about.180.degree. C.), which dramatically limits
the range of comonomers that can be reacted with sulfur to make
polymeric materials. By using nucleophilic activators, elemental
sulfur can be activated toward polymerization at lower temperatures
(T.ltoreq.130.degree. C.) and at lower concentrations, which allows
for polymerizations to be performed in organic solvent and
potentially aqueous media. Since co-solvents can be used for the
first time, a wide host of commercially available comonomers, such
as vinylic comonomers (e.g. styrenic compounds) may be utilized to
expand the functionality of sulfur copolymers that can be prepared.
Expanding this scope of chemical functionality in the sulfur
copolymer may result in sulfur materials having new and improved
physical properties (e.g., improved electrical conductivity,
improved barrier properties as coatings, water solubility, and
flame retardancy). These materials may be used as electrode
materials in Li-batteries (specifically, cathode materials in Li--S
batteries) and is various specialty polymer applications (e.g.,
lubricants, adhesives, antioxidants, coatings).
In an embodiment of the present invention, nucleophilic activators
comprising amine- or heteroatom- (e.g., nitrogen, sulfur, oxygen)
containing aromatic or heterocyclic compounds may be used to
activate elemental sulfur (S.sub.8), which allows for a wider scope
of synthetic conditions and comonomers that can copolymerize with
elemental sulfur to form functional sulfur copolymers. Inexpensive
activators and vinylic comonomers may be used in making a diverse
family of polymer products which are otherwise inaccessible without
the activation elemental sulfur. For example, the nucleophilic
activators may be used in free radical copolymerizations of S.sub.8
with styrenics (e.g., styrene), acrylates, and methacrylates.
Non-limiting examples of nucleophilic activators include, but are
not limited to, imidazoles, functional imidazoles, anilines,
aminostyrene derivatives, 1,4-diazabicyclo[2.2.2]octane (DABCO),
1,8-diazabicyclo[5.4.0.] undec-7-ene (DBU), nucleophilic
heterocycles such as N-heterocyclic carbenes, phosphines, and other
widely used nucleophilic organocatalysts.
In further embodiments, these amine containing compounds may also
be used as both the activator and the comonomer, which enables the
formation of sulfur copolymers that carry amine functional groups
or other nucleophilic functional groups into the copolymer
material. These amine functional groups may be used in further
post-polymerization modifications. For instance, the amine
functional sulfur copolymer can be reacted with other inexpensive
comonomers, such as epoxies, to make copolymers with a high content
of sulfur and with improved mechanical properties.
It is another objective of the present invention to provide
polymeric materials that have a high refractive index of n>2.0
in the visible and mid-IR regimes, high transparency in the mid-IR
regime, and that can be amenable to melt and solution processing
into lenses, films, or optical fibers. The present invention
features a novel composition and process of incorporating selenium
units into polymeric materials by using and copolymerizing cyclic
selenium sulfides, which is a comonomer ring system that possesses
both sulfur and selenium, with other comonomers. The use of cyclic
selenium sulfides allows for easier and more controllable
incorporation of Se to afford chalcogenide hybrid copolymers with
refractive indices aboven>2.0, which is the key benchmark to
warrant use of these polymeric transmitting materials in IR thermal
imaging as lenses, windows and other devices.
In one embodiment, the present invention features compositions and
methods of making a chalcogenide copolymer comprising one or more
cyclic selenium sulfide monomers having the formula
Se.sub.nS.sub.(8-n), wherein the cyclic selenium sulfide monomers
comprises at most about 70 wt % of selenium; and one or more
comonomers each selected from a group consisting of amine
comonomers, thiol comonomers, sulfide comonomers, alkynylly
unsaturated comonomers, epoxide comonomers, nitrone comonomers,
aldehyde comonomers, ketone comonomers, thiirane comonomers,
ethylenically unsaturated comonomers, styrenic comonomers, vinylic
comonomers, methacrylate comonomers, and acrylonitrile comonomers
at a level in the range of about 5-50 wt % of the chalcogenide
copolymer. In preferred embodiments, the chalcogenide copolymer has
a refractive index of about 1.7-2.6 at a wavelength in a range of
about 500 nm to about 8 .mu.m. In some embodiments, the
chalcogenide copolymer may further comprise one or more sulfur
monomers, at a level of about 5-50 wt % of the chalcogenide
copolymer. In still other embodiments, the chalcogenide copolymer
may further comprise elemental selenium (Se.sub.8), at a level of
about 5-50 wt % of the chalcogenide copolymer.
One of the unique inventive technical features of the present
invention is the use of cyclic selenium sulfide as an inexpensive
single source precursor for both selenium and sulfur units that can
be incorporated into high refractive index materials. The present
invention has surprisingly discovered that cyclic selenium sulfides
can be used as a comonomer for copolymerizations with organic
comonomers. Furthermore, copolymerizations of cyclic selenium
sulfides with either S.sub.8 or Se.sub.8 can initially be conducted
to tune the chalcogenide composition of Se and S units, followed by
addition of an organic comonomer to form terpolymers, or more
complex copolymer compositions. Without wishing to limit the
invention to any theory or mechanism, it is believed that this
technical feature of the present invention advantageously provides
for an optical copolymer having a high refractive index as compared
to other polymers. None of the presently known prior references or
works have used the unique inventive technical feature of the
present invention for preparing polymers or use in IR thermal
imaging.
Furthermore, the sulfur polymer of the present invention may have
the ability to self-heal upon reprocessing. Without wishing to
limit the present invention to any particular theory or mechanism,
it is believed that the self-healing property of these polymers are
due to their reversible S--S bonds, which allows for broken S--S
bonds to be reconnected by methods such as heat processing. Any
article constructed from the sulfur polymers may be reprocessable
and repairable.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention will become
apparent from a consideration of the following detailed description
presented in connection with the accompanying drawings in
which:
FIG. 1 shows a reaction schematic of a sulfur ring (S.sub.8)
opening and polymerizing.
FIG. 2 shows non-limiting examples of functional styrenic
comonomers that can copolymerize with sulfur by inverse
vulcanization.
FIG. 3 shows GPC data for examples of styrenic comonomers.
FIG. 4 shows an exemplary reaction mechanism for stabilization of
polymeric sulfur radicals in styrene copolymerization. The key
intermediate is the formation of primary methyl radical via the
propagation reactions to a substituted side of the vinyl or
reversible thiol-ene processes. Both can result in radicals that
abstract hydrogen atoms from the polymer backbone, resulting in
branching and cyclic S--S bonds.
FIG. 5 shows another reaction schematic for copolymerizing sulfur
and styrene.
FIG. 6 shows an example of a sulfur-styrenic copolymer of the
present invention. GPC data comparing results taken one year from
the initial results for a sulfur-styrenic copolymer demonstrates
that the copolymer is a stable polymer.
FIG. 7 shows a reaction schematic of epoxide comonomers
polymerizing with a sulfur copolymer formed using phenylenediamine
comonomers, and resulting in a termonomer. The amine functional
groups of the sulfur copolymer are free to react with the epoxide
functional groups of the epoxide monomers.
FIG. 8 shows a reaction schematic of epoxide comonomers
polymerizing with a sulfur copolymer formed using vinylaniline
comonomers, and resulting in a termonomer.
FIG. 9 shows samples of a sulfur copolymer (left) reacting with a
second comonomer (middle) to form a terpolymer (right).
FIG. 10 shows a polymerization reaction scheme of homopolymerizing
or non-homopolymerizing monomers. Non-limiting examples thereof are
also shown.
FIG. 11 shows an exemplary copolymerization reaction scheme of
sulfur and ethylenically unsaturated monomers. Non-limiting
examples of non-homopolymerizing monomers are also provided.
FIG. 12 shows .sup.1H NMR spectroscopic evidence of S.sub.8-allylic
copolymer formation.
FIG. 13 shows a cycling experiment (C/10 and C/5) comparing
sulfur-styrenic polymers and elemental sulfur as cathodes for
electrochemical cells. Excellent retention of charge capacity in
Li--S batteries is demonstrated when poly(sulfur-random-styrene)
copolymers are used as active cathode material.
FIG. 14 shows an exemplary reaction scheme of sulfur
copolymerization using nucleophilic activators according to an
embodiment of the present invention. Unlike the known methods of
free radical ring-opening polymerization of S.sub.8, which require
high temperatures in bulk molten sulfur, the proposed synthetic
scheme for polymerization processes via the nucleophilic activation
of S.sub.8 with amines, or amine functional comonomers, can be done
at relatively lower temperatures.
FIG. 15 shows non-limiting examples of heterocyclic amines as
nucleophilic activators.
FIG. 16 shows non-limiting and exemplary reaction schemes using a
sulfur-activator intermediate (1) in an electrophilic aromatic
substitution reaction with 1,3-phenylenediamines (PDA) (b), and
free radical polymerization (c) with vinylaniline to form amine
functional sulfur copolymers. Reaction (d) shows a reaction scheme
of reversible ring-opening of S.sub.8 with nucleophilic activators
to form reactive sulfobetaine intermediates.
FIG. 17 shows infrared lenses constructed from materials of prior
arts.
FIG. 18 shows an exemplary reaction schematic of elemental selenium
and elemental sulfur polymerizing with comonomers to form
chalcogenide-based copolymers with high Se and S content and high
refractive index.
FIG. 19 shows an exemplary reaction schematic of cyclic selenium
sulfides and elemental sulfur polymerizing with comonomers to form
chalcogenide-based copolymers with high Se and S content. Further
depicted are exemplary applications of said chalcogenide copolymers
in IR thermal imaging.
FIG. 20 shows an exemplary reaction schematic of cyclic selenium
sulfides and elemental sulfur polymerizing with comonomers to form
chalcogenide-based copolymers.
FIG. 21A shows an example of chalcogenide-based sulfur
copolymer.
FIG. 21B depicts an IR imaging through an optical substrate
containing a chalcogenide-based sulfur copolymer.
FIG. 22 shows a chart of refractive index vs. wavelength of
chalcogenide-based copolymers having varying compositions.
FIG. 23 shows examples of reaction schemes for sulfur copolymers
with improved thermomechanical properties and high refractive
indexes.
FIG. 24 shows various products prepared from a sulfur
prepolymer.
FIG. 25 shows a set of spin-coated films.
FIG. 26 shows various applications in which the sulfur copolymers
of the present invention may be utilized.
FIG. 27 is a cross-sectional micrograph of a poly(S-r-DIB)
copolymer layer (2.6 .mu.m in thickness) formed on a polyimide
layer (270 nm) on a glass substrate.
FIG. 28 shows a non-limiting example of Young's Modulus for a
pristine and a self-healed sulfur copolymers having 20 wt %
diisopropenylbenzene (DIB).
FIG. 29 shows a non-limiting example of a stress-strain curve for
sulfur copolymers.
FIG. 30 shows a digital image of lenses (left) poly(S-r-DIB) with
80 wt % S.sub.8 and (right) glass to demonstrate the enhanced
focusing power of the poly(S-r-DIB) lens afforded by the increased
refractive index.
FIG. 31 shows a non-limiting example of infrared lens constructed
from a sulfur copolymer of the present invention.
FIG. 32 shows a graph of transparency for 80%-wt S.sub.8 and
DIB.
FIG. 33 shows a graph of transparency for a sulfur copolymer and
PMMA.
FIG. 34 shows a graph of refractive indexes for various polymers
and sulfur copolymers.
FIG. 35 shows mid-IR imaging with a sulfur copolymer lens.
FIG. 36 shows comparisons of pristine, damaged, and self-healed
sulfur copolymer lenses for visible and mid-IR imaging.
DESCRIPTION OF PREFERRED EMBODIMENTS
As used herein, sulfur can be provided as elemental sulfur, for
example, in powdered form. Under ambient conditions, elemental
sulfur primarily exists in an eight-membered ring form (S.sub.8)
which melts at temperatures in the range of 120.degree.
C.-130.degree. C. and undergoes an equilibrium ring-opening
polymerization (ROP) of the S.sub.8 monomer into a linear
polysulfane with diradical chain ends. As the person of skill in
the art will appreciate, while S.sub.8 is generally the most
stable, most accessible and cheapest feedstock, many other
allotropes of sulfur can be used (such as other cyclic allotropes,
derivable by melt-thermal processing of S.sub.8). Any sulfur
species that yield diradical or anionic polymerizing species when
heated as described herein can be used in practicing the present
invention.
As used herein, the term "sulfur polymer" generally refers to any
polymer or copolymer that contains sulfur monomers. Sulfur polymer
may be used interchangeably with sulfur copolymer, optical sulfur
copolymer or polymer, chalcogenide copolymer or polymer, sulfur
polymer composition, or sulfur terpolymer, unless specified
otherwise.
As used herein, a "styrenic comonomer" is a monomer that has a
vinyl functional group. The styrenic comonomer may comprise a
styrene and at least one reactive functional group. As known to one
of ordinary skill in the art, a styrene is a derivative of benzene
ring that has a vinylic moiety. The sulfur diradicals can link to
the vinylic moieties of the styrenic commoners to form the
sulfur-styrenic polymer. In certain embodiments, the reactive
functional group may be a halogen, an alkyl halide, an alkyl, an
alkoxy, an amine, or a nitro functional group. Non-limiting
examples of styrenic comonomers include bromostyrene,
chlorostyrene, fluorostyrene, (trifluoromethyl)styrene,
vinylaniline, acetoxystyrene, methoxystyrene, ethoxystyrene,
methylstyrene, nitrostyrene, vinylbenzoic acid, vinylanisole, and
vinylbenzyl chloride.
As used herein, the term "amine monomer" is a monomer that has an
amine functional group. In one embodiment, aromatic amines and
multi-functional amines may be used. Amine monomers include, but
are not limited to, aromatic amines, vinylaniline,
m-phenylenediamine, and p-phenylenediamine. The various types of
phenylenediamines are inexpensive reagents due to their wide-spread
use in the preparation of many conventional polymers, e.g.,
polyureas, polyamides.
As used herein, the term "thiol monomer" is a monomer that has a
thiol functional group. Thiol monomers include, but are not limited
to, 4,4'-thiobisbenzenethiol and the like. The term "sulfide
monomers" are monomers that have sulfide functional groups.
As used herein, an alkynylly unsaturated monomer is a monomer that
has an alkynylly unsaturated functional group (i.e. triple bond).
The term "alkynylly unsaturated monomer" does not include compounds
in which the alkynyl unsaturation is part of a long chain alkyl
moiety (e.g., unsaturated fatty acids, or carboxylic salts, or
esters such as oleates, and unsaturated plant oils). In one
embodiment, aromatic alkynes, both internal and terminal alkynes,
multi-functional alkynes may be used. Examples of alkynylly
unsaturated monomers include, but are not limited to,
ethynylbenzene, 1-phenylpropyne, 1,2-diphenylethyne,
1,4-diethynylbenzene, 1,4-bis(phenylethynyl)benzene, and
1,4-diphenylbuta-1,3-diyne.
As used herein, the term "nitrone monomer" is a monomer that has a
nitrone groups. In one embodiment, nitrones, dinitrones, and
multi-nitrones may be used. Examples include, but are not limited
to, N-benzylidene-2-methylpropan-2-amine oxide.
As used herein, an "aldehyde monomer" is a monomer that has an
aldehyde functional group. In one embodiment, aldehydes,
dialdehydes, and multi- aldehydes may be used.
As used herein, the term "ketone monomer" is a monomer that has a
ketone functional group. In one embodiment, ketones, di-ketones,
and multi-ketones may be used.
As used herein, the term "epoxide monomer" is a monomer that has
epoxide functional groups. Non-limiting examples of such monomers
include, generally, mono- or polyoxiranylbenzenes, mono- or
polyglycidylbenzenes, mono- or polyglycidyloxybenzenes, mono- or
polyoxiranyl(hetero)aromatic compounds, mono- or
polyglycidyl(hetero)aromatic compounds, mono- or
polyglycidyloxy(hetero)aromatic compounds, diglycidyl bisphenol A
ethers, mono- or polyglycidyl(cyclo)alkyl ethers, mono- or
polyepoxy(cyclo)alkane compounds and oxirane-terminated oligomers.
In one preferred embodiment, the epoxide monomers may be benzyl
glycidyl ether and tris(4-hydroxyphenyl)methane triglycidyl ether.
In certain embodiments, the epoxide monomers may include a
(hetero)aromatic moiety such as, for example, a phenyl, a pyridine,
a triazine, a pyrene, a naphthalene, or a polycyclic
(hetero)aromatic ring system, bearing one or more epoxide groups.
For example, in certain embodiments, the one or more epoxide
monomers are selected from epoxy(hetero)aromatic compounds, such as
styrene oxide and stilbene oxide and (hetero)aromatic glycidyl
compounds, such as glycidyl phenyl ethers (e.g., resorcinol
diglycidyl ether, glycidyl 2-methylphenyl ether), glycidylbenzenes
(e.g., (2,3-epoxypropyl)benzene) and glycidyl heteroaromatic
compounds (e.g., N-(2,3-epoxypropyl)phthalimide). In certain
desirable embodiments, an epoxide monomer will have a boiling point
greater than 180.degree. C., greater than 200.degree. C., or even
greater than 230.degree. C. at the pressure at which polymerization
is performed (e.g., at standard pressure, or at other
pressures).
As used herein, the term "thiirane monomer" is a monomer that has a
thirane functional group. Non-limiting examples of thiirane
monomers include, generally, mono- or polythiiranylbenzenes, mono-
or polythiiranylmethylbenzenes, mono- or
polythiiranyl(hetero)aromatic compounds, mono- or
polythiiranylmethyl(hetero)-aromatic compounds, dithiiranylmethyl
bisphenol A ethers, mono- or polydithiiranyl (cyclo)alkyl ethers,
mono- or polyepisulfide(cyclo)alkane compounds, and
thiirane-terminated oligomers. In some embodiments, thiirane
monomers may include a (hetero)aromatic moiety such as, for
example, a phenyl, a pyridine, a triazine, a pyrene, a naphthalene,
or a poly cyclic (hetero)aromatic ring system, bearing one or more
thiirane groups. In certain desirable embodiments, a thiirane
monomer can have a boiling point greater than 180.degree. C.,
greater than 200.degree. C., or even greater than 230.degree. C. at
the pressure at which polymerization is performed (e.g., at
standard pressure).
As used herein, an ethylenically unsaturated monomer is a monomer
that contains an ethylenically unsaturated functional group (i.e.
double bond). The term "ethylenically unsaturated monomer" does not
include compounds in which the ethylenic unsaturation is part of a
long chain alkyl moiety (e.g. unsaturated fatty acids such as
oleates, and unsaturated plant oils).
Non-limiting examples of ethylenically unsaturated monomers include
vinyl monomers, acryl monomers, (meth)acryl monomers, unsaturated
hydrocarbon monomers, and ethylenically-terminated oligomers.
Examples of such monomers include, generally, mono- or
polyvinylbenzenes, mono- or polyisopropenylbenzenes, mono- or
polyvinyl(hetero)aromatic compounds, mono- or
polyisopropenyl(hetero)-aromatic compounds, acrylates,
methacrylates, alkylene di(meth)acrylates, bisphenol A
di(meth)acrylates, benzyl (meth)acrylates, phenyl(meth)acrylates,
heteroaryl (meth)acrylates, terpenes (e.g., squalene) and carotene.
In some embodiments, non-limiting examples of ethylenically
unsaturated monomers that are non-homopolymerizing include allylic
monomers, isopropenyls, maleimides, norbornenes, vinyl ethers, and
methacrylonitrile. In other embodiments, the ethylenically
unsaturated monomers may include a (hetero)aromatic moiety such as,
for example, phenyl, pyridine, triazine, pyrene, naphthalene, or a
polycyclic (hetero)aromatic ring system, bearing one or more
vinylic, acrylic or methacrylic substituents. Examples of such
monomers include benzyl (meth)acrylates, phenyl (meth)acrylates,
divinylbenzenes (e.g., 1,3-divinylbenzene, 1,4-divinylbenzene),
isopropenylbenzene, styrenics (e.g., styrene, 4-methylstyrene,
4-chlorostyrene, 2,6-dichlorostyrene, 4-vinylbenzyl chloride),
diisopropenylbenzenes (e.g., 1,3-diisopropenylbenzene),
vinylpyridines (e.g., 2-vinylpyridine, 4-vinylpyridine),
2,4,6-tris((4-vinylbenzyl)thio)-1,3,5-triazine and divinylpyridines
(e.g., 2,5-divinylpyridine). In certain embodiments, the
ethylenically unsaturated monomers (e.g., including an aromatic
moiety) bear an amino (i.e., primary or secondary) group, a
phosphine group or a thiol group. One example of such a monomer is
vinyldiphenylphosphine. In certain desirable embodiments, an
ethylenically unsaturated monomer will have a boiling point greater
than 180.degree. C., greater than 200.degree. C., or even greater
than 230.degree. C. at the pressure at which polymerization is
performed (e.g., at standard pressure).
As used herein, the term "self-healing" is defined as to enable a
material to repair damage with minimum intervention. In some
embodiments, mechanisms and techniques to enable self-healing may
include covalent bonding, supramolecular chemistry, H-bonding,
ionic interactions, .pi.-.pi. stacking, chemo-mechanical repairs
focusing on encapsulation, remote self-healing, or shape memory
assisted polymers. In one preferred embodiment, self-healing
utilizes thermal reformation. As used herein, thermal reformation
involves the use of heat to reform the bonds or cross-links of a
polymeric material.
As used herein, "non-homopolymerizing" refers to the same monomers
that do not readily polymerize with each other. For example,
non-homopolymerizing monomers may be held at a temperature of at
least 100.degree. C. for period of time, such as 10 to 100 hours,
without forming increasing quantities of a homopolymer. This is not
to say that the homopolymer never forms or would not do so under
different reaction conditions; however, the homopolymer would
depolymerize at a rate greater than the rate of homopolymer
formation and an increasing quantity of homopolymer is not
observed. As another example, monomers exhibiting no tendency to
homopolymerize are monomers that do not polymerize to more than
about 5% conversion of monomer to polymer at a temperature of at
least 100.degree. C. for period of time, such as 10 to 100 hours.
Non-homopolymerizing monomers are known to one of ordinary skill in
the art.
As used herein, a high molecular weight polymer can have a molar
mass of at least 2,000 g/mol, for example, about 5,000 g/mol or
higher. The term "wt %", which is interchangeable with % wt, refers
to a weight percent of a component with respect to the sulfur
polymer, unless otherwise specified.
As used herein, the term "functional" in correlation with a polymer
refers to functional polymers that have specified physical,
chemical, biological, pharmacological, or other properties or uses
that are determined by the presence of specific chemical functional
groups, which are usually dissimilar to those of the backbone chain
of the polymer.
As used herein, the term "nucleophilic activator" may be defined as
an activator that can react with sulfur via a nucleophilic, or
anionic mechanism, to ring-open the S.sub.8-elemental sulfur and
form reactive sulfur intermediates, such as a linear sulfobetaine
intermediate. A nucleophilic mechanising is a mechanism in which an
electron pair is donated to an electrophile to form a chemical
bond. In nucleophilic activation, an electron nucleophile bonds
with the positive or partially positive charge of an atom or a
group of atoms. The mechanisms of reactions such as electrophilic
substitutions, electrophilic aromatic substitutions, and free
radical polymerizations are known to one of ordinary skill in the
art.
As used herein, the term "chalcogenide" refers to a compound
containing one or more chalcogen elements. One of ordinary skill in
the art will understand that the classical chalcogen elements are
sulfur, selenium and tellurium. In accordance with the present
invention, the use of chalcogenide refers to compounds and/or
polymers containing selenium.
As known to one of ordinary skill in the art, the term "isomer"
refers to compounds having the same formula but differ in
arrangement. For instance, isomers of cyclic selenium sulfides,
such as Se.sub.2S.sub.6 and Se.sub.3S.sub.5, can have different
placements of the Se units in the ring (e.g., S--Se--Se--S or
S--Se--S). Isomers of Se.sub.2S.sub.6 include 1,2-isomers,
1,3-isomers, 1,4-isomers, and 1,5-isomers, wherein the numbers
refer to the position of the Se units in the eight-membered
ring.
As known to one of ordinary skill in the art, the term "visible"
refers to a portion of the electromagnetic spectrum that falls in
the range of 390 to 700 nm. As used herein, the term "infrared"
(IR) refers to a portion of the electromagnetic spectrum that falls
in the range of 700 nm to 1 mm. Subsets of the IR spectrum include
near-IR (700 nm to 3 .mu.m), mid-IR (3-8 .mu.m), long-wavelength IR
(8-15 .mu.m) and far-IR (15 .mu.m to 1 mm).
As used herein, the terms "those defined above" and "those defined
herein" when referring to a variable incorporates by reference the
broad definition of the variable as well as any narrow and/or
preferred, more preferred and most preferred definitions, if
any.
Styrenics and Unconventional Comonomers
Referring now to FIG. 1-13, one embodiment of the present invention
features a sulfur polymer comprising one or more sulfur monomers at
between about 10 to 95% wt of the polymer, and one or more styrenic
comonomers at between about 5 to 90% wt of the polymer. The
styrenic comonomers can comprise one or more functional groups. In
preferred embodiments, the styrenic comonomers are polymerized with
the sulfur monomers via chain transferring of a benzylic hydrogen
of the styrenic comonomers to link sulfur radicals, formed via
chain braking of the sulfur monomers, to a vinyl moiety of the
styrenic comonomers. This surprising polymerization mechanism for
the preparation of chemically stable and processable sulfur based
copolymers via the reaction of liquid elemental sulfur and styrenic
comonomers is described herein.
In some embodiments, the sulfur monomers are between about 10 to
30% wt of the polymer, 30 to 40% wt of the polymer, 40 to 60% wt of
the polymer, 60 to 80% wt of the polymer, or 80 to 95% wt of the
polymer. For example, the sulfur monomers are at least about 50% wt
of the polymer. In other embodiments, the styrenic comonomers are
between about 5 to 20% wt of the polymer, 20 to 40% wt of the
polymer, 40 to 60% wt of the polymer, 60 to 80% wt of the polymer,
or 80 to 90% wt of the polymer. For example, the styrenic monomers
are at most about 50% wt of the polymer.
In some embodiments, the one or more functional groups are selected
from a group consisting of a halogen functional group, an amine
functional group, an alkyl functional group, an alkyl halide
functional group, an alkoxyl functional group, a phenyl functional
group, a nitro functional group. In other embodiments, the
functional groups may be carboxylic acids, carboxylate salts,
sulfonic acids, sulfonate salts, quaternary ammonium salts, ethers,
oligo-ethers, polyethers, polyamines, esters, amides, and alcohols.
In one embodiment, the halogen functional group is selected from a
group consisting of Br, Cl, and F. In another embodiment, the alkyl
halide functional group comprises one or more moieties of Br, Cl,
or F. In a further embodiment, the alkoxyl functional group
comprises --OCH.sub.3, --COOH, or --COOR.
In some embodiments, the sulfur polymer further comprises one or
more functional termonomers at between about 5 to 50% wt of the
polymer. In other embodiments, the functional termonomers are
between about 5 to 15% wt of the polymer, 15 to 25% wt of the
polymer, 25 to 35% wt of the polymer, or 35 to 50% wt of the
polymer. Preferably, each functional termonomers has at least one
polymerizable moiety. In another embodiment, each functional
termonomers has two or more polymerizable moieties. The
polymerizable moiety of the functional termonomers can be linked to
the functional group of the styrenic comonomers. Non-limiting
examples of functional termonomers include a vinyl monomer, an
isopropenyl monomer, an acryl monomer, a methacryl monomer, an
unsaturated hydrocarbon monomer, an epoxide monomer, a thiirane
monomer, an alkynyl monomer, a diene monomer, a butadiene monomer,
an isoprene monomer, a norbornene monomer, an amine monomer, a
thiol monomer, a sulfide monomer, an alkynylly unsaturated monomer,
a nitrone monomer, an aldehyde monomer, a ketone monomer, and an
ethylenically unsaturated monomer.
In other embodiments, the styrenic comonomers are water-soluble.
The sulfur monomers and styrenic comonomers can be polymerized in
an aqueous solution. An example of the aqueous solution is
water.
The sulfur polymer can be made, for example, by polymerization of
molten sulfur with the styrenic comonomers. Thus, in one aspect,
the invention provides a method for making the sulfur polymer as
described above. For example, in one embodiment, the method
includes heating a mixture including sulfur and the styrenic
comonomers together at a temperature in the range of about
120.degree. C. to about 230.degree. C., e.g., in the range of about
120.degree. C. to about 150.degree. C. The person of skill in the
art will select conditions that provide the desired level of
polymerization. In certain embodiments, the polymerization reaction
is performed under ambient pressure. However, in other embodiments,
the polymerization reaction can be performed at elevated pressure
(e.g., in a bomb or an autoclave). Elevated pressures can be used
to polymerize more volatile comonomers, so that they do not
vaporize under the elevated temperature reaction conditions.
According to one embodiment, the present invention features a
method of synthesizing a stable sulfur polymer. The method may
comprise providing elemental sulfur; providing one or more styrenic
monomers, wherein the styrenic monomers comprise at least one vinyl
moiety and one or more functional groups; providing a nucleophilic
activator; melting the elemental sulfur to form liquid sulfur;
adding the nucleophilic activator to the liquid sulfur, wherein the
nucleophilic activator catalyzes ring-opening of the liquid sulfur
via nucleophilic activation, thereby forming sulfur radicals;
adding the styrenic comonomers to the sulfur radicals; and
polymerizing the styrenic comonomers with the sulfur radicals,
thereby forming the stable sulfur polymer. Without wishing to limit
the invention to a particular theory or mechanism, the nucleophilic
activator can increase a rate of polymerization of the styrenic
comonomers and the sulfur radicals by a factor of about 2-100 as
compared to the rate of polymerization without the nucleophilic
activator. Furthermore, the nucleophilic activator enables the
polymerization of the styrenic comonomers with the sulfur radicals
to occur at a temperature of about 110-130.degree. C., for example,
about 120.degree. C. Examples of nucleophilic activators include,
but are not limited to, amine-containing compounds,
nitrogen-containing heterocycles, sulfide-containing compounds,
imidazoles, functional imidazoles, anilines, aminostyrene
derivatives, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),
1,4-diazabicyclo[2.2.2]octane (DABCO), nucleophilic heterocycles,
N-heterocyclic carbenes, phosphines, ionic liquids, thiols, ureas,
and nucleophilic organocatalysts.
It is theorized that polymerization occurs by chain transferring a
benzylic hydrogen of the styrenic comonomer to link the sulfur
radical to the vinyl moiety of the styrenic comonomer. The styrenic
comonomers can copolymerize with molten liquid sulfur to form
stable copolymers via chain transfer of benzylic hydrogen in the
copolymer backbone. Without wishing to limit the invention to a
particular theory or mechanism, the chain transfer of benzylic
hydrogen can enable introduction of branching to suppress
depolymerization, presumably through looping of growing sulfur
radicals to form cyclic polysulfides.
Another to embodiment of the present invention features a method of
synthesizing a stable sulfur polymer. The method may comprise
providing elemental sulfur, providing one or more styrenic monomers
comprising a vinyl moiety and one or more functional groups,
melting the elemental sulfur to form a liquid solution of sulfur
diradicals, adding the styrenic comonomers to the liquid solution;
and polymerizing the styrenic comonomers with the sulfur radicals
by chain transferring a benzylic hydrogen of the styrenic
comonomers to link the sulfur radicals to the vinyl moiety, thereby
forming the stable sulfur polymer. In some embodiments, the step of
polymerizing the styrenic comonomers with the sulfur radicals is
performed at a temperature of between about 120-230.degree. C.,
e.g., in the range of about 120-150.degree. C., or about
150-170.degree. C., or about 170-190.degree. C., or about
190-210.degree. C., or about 210-230.degree. C.
In other embodiments, the method may further comprise grafting one
or more functional termonomers to the sulfur polymer by linking a
polymerizable moiety of the functional termonomers to the
functional group of the styrenic comonomers. Non-limiting examples
of the functional termonomers may include a vinyl monomer, an
isopropenyl monomer, an acryl monomer, a methacryl monomer, an
unsaturated hydrocarbon monomer, an epoxide monomer, a thiirane
monomer, an alkynyl monomer, a diene monomer, a butadiene monomer,
an isoprene monomer, a norbornene monomer, an amine monomer, a
thiol monomer, a sulfide monomer, an alkynylly unsaturated monomer,
a nitrone monomer, an aldehyde monomer, a ketone monomer, and an
ethylenically unsaturated monomer. Other examples of functional
termonomers may include aniline monomers, thiophene monomers, and
pyrrole monomer, which can be monomers for making conductive
polymers.
In some embodiments, the step of grafting one or more functional
termonomers to the sulfur polymer may further comprise dissolving
the sulfur polymer and the functional termonomers in a solvent and
adding an initiating agent to the solvent, which promotes
copolymerization of the sulfur polymer and the functional
termonomers. Preferably, the solvent is a biphasic mixture from a
non-polar solvent, such as tetrahydrofuran (THF) and water. In
other embodiments, the solvent comprises water. Non-limiting
examples of initiating agents include ammonium persulfate (APS) and
potassium persulfate, FeCl.sub.3, and related complexes.
In some embodiments, the sulfur polymer can be modified by reacting
an available reactive functional group on the functional styrenic
comonomer with a terpolymer to form a new copolymer material. The
technique of reacting may be oxidative coupling, copolymerization,
or any appropriate method of polymerization. Non-limiting
techniques of polymerization includes free radical polymerization,
controlled radical polymerization, ring-opening polymerization,
ring-opening metathesis polymerization, step-growth polymerization,
or chain-growth polymerization.
An alternate embodiment of the present invention features a method
of synthesizing a dynamic, covalent sulfur polymer as described
herein. The method can comprise providing elemental sulfur,
providing one or more styrenic monomers comprising a vinyl moiety
and one or more functional groups, melting the elemental sulfur to
form a liquid solution of sulfur diradicals comprising dynamic
sulfur-sulfur (S--S) bonds, adding the styrenic comonomers to the
liquid solution, polymerizing the styrenic comonomers with the
sulfur radicals by chain transferring a benzylic hydrogen of the
styrenic comonomers to link the sulfur radicals to the vinyl
moiety, thereby forming the stable sulfur polymer, grafting a
functional conjugated copolymer to the sulfur polymer by linking a
polymerizable moiety of the functional conjugated copolymer to the
functional group of the styrenic comonomers, and dynamically
activating the dynamic S--S bonds by a stimulus to enable
re-processing or melt processing of the sulfur polymer. In one
embodiment, grafting of the functional conjugated copolymer to the
sulfur polymer can comprise dissolving the sulfur polymer and the
functional conjugated copolymer in a solvent and adding an
initiating agent to the solvent to initiate radical polymerization
of the sulfur polymer and the functional conjugated copolymer.
Preferably, the functional conjugated copolymer improves the
electrical conductivity of the sulfur polymer.
The stable formation of amine functional copolymers via the
copolymerization of elemental sulfur and 4-vinylaniline was
afforded in liquid sulfur and while using solution polymerizations
in arene solvents to form chemically stable copolymers. This
discovery is particularly surprising since amine groups were
previously known to degrade S--S bonds. These amine groups can be
introduced by direct copolymerization of 4-vinylaniline into the
copolymer without the need for protecting groups on the amine.
Post-polymerization modification of the amine-containing sulfur
polymers enables the creation of a new class of functional
terpolymer materials thru reactions of the pendant amine side chain
groups to form conductive polyaniline copolymers directly
conjugated to the sulfur polymer backbone. These new polymer
materials may be used in as high capacity electrodes for Li--S
batteries since the introduction of new functionalities such as
conductive polyaniline segments can increase the electrical
conductivity of these resultant materials.
For illustrative purposes, the following are non-limiting examples
of preparing a sulfur polymer, in particular, a sulfur-styrenic
polymer.
Example 1. Non-Limiting Procedure for Preparing an Exemplary Sulfur
Polymer
To a 25 mL vial equipped with a magnetic stir bar was loaded with
sulfur (700 mg, 2.73 mmol) and 4-vinylaniline (300 mg, 2.52 mmol).
The mixture was heated in an oil bath and stirred at a temperature
of about 130.degree. C. to yield a red-orange liquid. The reaction
was cooled to yield a poly(S-r-vinylaniline).
Example 2. Non-Limiting Procedure for Preparing an Exemplary Sulfur
Polymer Grafted to a Terpolymer
Referring to FIGS. 7 and 8, about 50 mg of poly(S-r-vinylaniline)
was added to a solvent of 5 ml tetrahydrofuran and 2 ml water, as
shown in FIG. 8A. About 50 mg of aniline was added to the
poly(S-r-vinylaniline) and solvent mixture, followed by 420 mg (2.5
eq) of ammonium persulfate ((NH.sub.4).sub.2S.sub.2O.sub.8), as
shown in FIG. 8B. The resulting polymer is a
poly(S-r-vinylaniline)-graft-polyaniline, as shown in FIG. 8C.
In preferred embodiments, sulfur terpolymers and more complex
copolymer materials, such as in the form of cross-linked polymers
or non-crosslinked, intractable polymers, can be reprocessed by
stimuli activation of dynamic S--S bonds in the polymer material.
As used herein, the term "dynamic" is defined reversibly breaking
of bonds. The introduction of S--S bonds into an intractable
polymer material, or cross-linked polymer network, can allow for
re-processing of the polymer material due to dynamic breaking of
S--S bonds. In one embodiment, the sulfur polymers described herein
are dynamic covalent polymers. The dynamic covalent polymers may
comprise a terpolymer, or a more complex copolymer having S--S
bonds and some other copolymer segment that is intractable, or
cross-linked. Stimuli, such as thermal, light, or another form of
stimuli, can induce dynamic activation of S--S bonds to enable
re-processing, or melt processing of otherwise non-reversible,
processable polymeric materials.
As an example, polyaniline can often exist in forms that are
intractable, or difficult to melt process. The sulfur polymer of
the present invention may contain polyaniline and is cross-linked.
Since S--S bonds can become dynamic (i.e., reversibly break) at
temperatures of between about 60-100.degree. C.), the sulfur
polymer can be briefly heat pressed, which scrambles the S--S bonds
and sufficiently softens the material long enough to press into
films or other molded forms. Typical polymers such as thermosets,
cross-linked, and/or intractable polymers cannot be processed in
this manner; therefore fusion of typical polymers with S--S bonds
can make for new properties. For instance, new terpolymers, or more
complex copolymer material that introduces a conjugated copolymer,
such as polyaniline units, can improve the electrical conductivity
of the material, and can also be used as an active material in
cathodes for Li--S battery to increase the volumetric energy
density of the battery.
The use of a new electroactive cathode material for an Li--S
battery, which can be the sulfur polymer, upon discharge, generates
soluble additive species in situ that co-deposit onto the cathode
with lower sulfide discharge products. These additive species may
be introduced into the electroactive material during the synthesis
of the material, or added to the electrolyte or battery separator
as a soluble species. These additive species are able to co-deposit
with sulfide-containing discharge products via active
electrochemical reactions, or passive non-electrochemical
processes. Co-deposition of these additive species with sulfide
discharge products onto the Li--S cathode plasticizes the electrode
against mechanical fracture during battery charge-discharge
cycling. Plasticization enables retention of charge capacity and
improve cycle lifetime beyond 100 cycles. The electroactive
material in this case is best embodied by a copolymer material
comprising elemental sulfur and an organic comonomer. Upon
discharge of this copolymer, soluble organosulfur species are
formed which function to improve Li--S batteries as described
above.
An exemplary embodiment features an electrochemical cell comprising
an anode comprising metallic lithium, a cathode comprising any of
the aforementioned sulfur polymers that generate soluble additive
species in situ upon discharge and the soluble additive species
co-deposit with lower sulfide discharge products onto the cathode,
and a non-aqueous electrolyte interposed between the cathode and
the anode. In some embodiments, the lower sulfide discharge
products are Li.sub.2S.sub.3, Li.sub.2S.sub.2, or Li.sub.2S.
Preferably, the electrochemical cell has an increased volumetric
energy density. For example, the capacity of the electrochemical
cell ranges from about 200 to about 1200 mAh/g.
Any embodiment of the electrochemical cells may be used in electric
vehicle applications, portable consumer devices portable consumer
devices (e.g., Personal electronics, cameras, electronic
cigarettes, handheld game consoles, and flashlights), motorized
wheelchairs, golf carts, electric bicycles, electric forklifts,
tools, automobile starters, and uninterruptible power supplies.
In some embodiments, the electrolyte and/or a separator comprises
the sulfur polymer. The sulfur polymer generates soluble
organosulfur species upon discharge. The soluble additive species
are co-deposited with the lower sulfide discharge products by an
electrochemical reaction or a non-electrochemical reaction.
Alternative embodiments of the sulfur polymer may further comprise
one or more monofunctional monomers, or one or more polyfunctional
monomers (e.g., difunctional or trifunctional). The one or more
polyfunctional monomers is selected from a group consisting of a
polyvinyl monomer (e.g., divinyl, trivinyl), a polyisopropenyl
monomer (e.g., diisoprenyl, triisoprenyl), a polyacryl monomer
(e.g., diacryl, triacryl), a polymethacryl monomer (e.g.,
dimethacryl, trimethacryl), a polyunsaturated hydrocarbon monomer
(e.g., diunsaturated, triunsaturated), a polyepoxide monomer (e.g.,
diepoxide, triepoxide), a polythiirane monomer (e.g., dithiirane,
trithiirane), a polyalkynyl monomer, a polydiene monomer, a
polybutadiene monomer, a polyisoprene monomer, a polynorbornene
monomer, a polyamine monomer, a polythiol monomer, a polysulfide
monomer, a polyalkynylly unsaturated monomers, a polynitrone
monomers, a polyaldehyde monomers, a polyketone monomers, and a
polyethylenically unsaturated monomers.
In some embodiments, the one or more polyfunctional monomers is
selected from a group consisting of a divinylbenzene, a
diisopropenylbenzene, an alkylene di(meth)acrylate, a bisphenol A
di(meth)acrylate, a terpene, a carotene, a divinyl (hetero)aromatic
compound and a diisopropenyl (hetero)aromatic compound. In other
embodiments, a polyfunctional monomer can have one or more amine,
thiol, sulfide, alkynylly unsaturated, nitrone and/or nitroso,
aldehyde, ketone, thiirane, ethylenically unsaturated, and/or
epoxide moieties moieties; and one or more amine, thiol, sulfide,
alkynylly unsaturated, nitrone and/or nitroso, aldehyde, ketone,
thiirane, ethylenically unsaturated, and/or epoxide moieties,
wherein the first and second moieties are different. A non-limiting
example is a divinylbenzene monoxide.
In some embodiments, the one or more polyfunctional monomers are at
a level of about 2 to about 50 wt %, or about 2 to about 10 wt %,
or about 10 to about 20 wt %, or about 20 to about 30 wt %, or
about 30 to about 40 wt %, or about 40 to about 50 wt % of the
sulfur polymer. In other embodiments, the one or more
monofunctional monomers are at a level up to about 5 wt %, or about
10 wt %, or about 15 wt % of the sulfur polymer.
According to another embodiment, the present invention features a
sulfur polymer comprising about 10-95 wt % of sulfur monomers, and
about 5-50 wt % of non-homopolymerizing monomers. The
non-homopolymerizing monomers are copolymerize with the sulfur
monomers via free radical polymerization to form the sulfur
polymer. Preferably, the sulfur polymer has a molar mass of at
least 2,000 g/mole and is a functional polymer. In other
embodiments, the sulfur polymer comprises sulfur monomers at a
range of about 5 to 10 wt %, or about 10 to 20 wt %, or about 20 to
30 wt %, or about 30 to 40 wt %, or about 40 to 50 wt %, or about
50 to 60 wt %, or about 60 to 70 wt %, or about 70 to 80 wt %, or
about 80 to 95 wt % of the sulfur polymer. In some embodiments, the
sulfur polymer comprises the non-homopolymerizing monomers at a
range of about 5 to 10 wt %, or about 10 to 20 wt %, or about 20 to
30 wt %, or about 30 to 40 wt %, or about 40 to 50 wt % of the
sulfur polymer.
According to another embodiment, the present invention features a
sulfur polymer comprising about 10-95 wt % of sulfur copolymers,
and about 5-50 wt % of non-homopolymerizing monomers. The
non-homopolymerizing monomers are copolymerized with the sulfur
copolymers, via free radical polymerization, to form the sulfur
polymer. Preferably, the sulfur polymer has a molar mass of at
least 2,000 g/mole and is a functional polymer. In some
embodiments, the sulfur copolymer comprises sulfur monomers at
about 10-95 wt % of the sulfur copolymers, and one or more
comonomers at about 5-50 wt % of the sulfur copolymers. The
comonomers may be selected from a group consisting of amine
comonomers, thiol comonomers, sulfide comonomers, alkynylly
unsaturated comonomers, epoxide comonomers, nitrone comonomers,
aldehyde comonomers, ketone comonomers, thiirane comonomers,
ethylenically unsaturated comonomers, styrenic comonomers, vinylic
comonomers, acrylic comonomers, methacrylate comonomers, and
acrylonitrile comonomer. Preferably, the one or more comonomers are
copolymerized with the sulfur monomers to form the sulfur
copolymer. In still other embodiments, the sulfur copolymer
comprises one or more comonomers at a range of about 5 to 10 wt %,
or about 10 to 20 wt %, or about 20 to 30 wt %, or about 30 to 40
wt %, or about 40 to 50 wt % of the sulfur copolymer. In other
embodiments, the sulfur copolymer comprises sulfur monomers at a
range of about 5 to 10 wt %, or about 10 to 20 wt %, or about 20 to
30 wt %, or about 30 to 40 wt %, or about 40 to 50 wt %, or about
50 to 60 wt %, or about 60 to 70 wt %, or about 70 to 80 wt %, or
about 80 to 95 wt % of the sulfur copolymer.
In some embodiments, the non-homopolymerizing monomers are
ethylenically unsaturated monomers, such as maleimide monomers,
norbornene monomers, allylic monomers, monomers having at least one
vinyl ether moiety, and monomers having at least one isopropenyl
moiety. In other embodiments, the non-homopolymerizing monomers can
react with sulfur radicals of the sulfur monomers via a thiol-ene
reaction or other related processes. For example, the thiol-ene
reaction involves the thiolation of a C--C double bond followed by
a proton-exchange. In accordance with the present invention, a
sulfur radical reacts with a C--C double bond of the
non-homopolymerizing monomer. In still other embodiments, the
non-homopolymerizing monomers can react with sulfur copolymer
radicals of the sulfur copolymers via the thiol-ene reaction or
other related processes. For example, a sulfur copolymer radical
reacts with a C--C double bond of the non-homopolymerizing
monomer.
In yet other embodiments, the sulfur polymer may further comprise
one or more termonomers selected from a group consisting of a vinyl
monomer, an isopropenyl monomer, an acryl monomer, a methacryl
monomer, an unsaturated hydrocarbon monomer, an epoxide monomer, a
thiirane monomer, an alkynyl monomer, a diene monomer, a butadiene
monomer, an isoprene monomer, a norbornene monomer, an amine
monomer, a thiol monomer, a sulfide monomer, an alkynylly
unsaturated monomer, a nitrone monomer, an aldehyde monomer, a
ketone monomer, an ethylenically unsaturated monomer, or a styrenic
monomer. The termonomers may be present in an amount ranging from
about 5 to 50 wt % of the sulfur polymer. For instance, the one or
more termonomers are at a level of about 5 to about 10 wt %, or
about 10 to about 20 wt %, or about 20 to about 30 wt %, or about
30 to about 40 wt %, or about 40 to about 50 wt % of the sulfur
polymer.
Alternative embodiments of the sulfur polymers may further comprise
one or more polyfunctional monomers (e.g., difunctional or
trifunctional). The one or more polyfunctional monomers can be
selected from a group consisting of a polyvinyl monomer (e.g.,
divinyl, trivinyl), a polyisopropenyl monomer (e.g., diisoprenyl,
triisoprenyl), a polyacryl monomer (e.g., diacryl, triacryl), a
polymethacryl monomer (e.g., dimethacryl, trimethacryl), a
polyunsaturated hydrocarbon monomer (e.g., diunsaturated,
triunsaturated), a polyepoxide monomer (e.g., diepoxide,
triepoxide), a polythiirane monomer (e.g., dithiirane,
trithiirane), a polyalkynyl monomer, a polydiene monomer, a
polybutadiene monomer, a polyisoprene monomer, a polynorbornene
monomer, a polyamine monomer, a polythiol monomer, a polysulfide
monomer, a polyalkynylly unsaturated monomer, a polynitrone
monomer, a polyaldehyde monomer, a polyketone monomer, and a
polyethylenically unsaturated monomer. In some embodiments, the one
or more polyfunctional monomers is selected from a group consisting
of a divinylbenzene, a diisopropenylbenzene, an alkylene
di(meth)acrylate, a bisphenol A di(meth)acrylate, a terpene, a
carotene, a divinyl (hetero)aromatic compound and a diisopropenyl
(hetero)aromatic compound.
The polyfunctional monomers may be present in an amount ranging
from about 5 to 50 wt % of the sulfur polymer. In some embodiments,
the one or more polyfunctional monomers are at a level of about 5
to about 10 wt %, or about 10 to about 20 wt %, or about 20 to
about 30 wt %, or about 30 to about 40 wt %, or about 40 to about
50 wt % of the sulfur polymer. In some embodiments, the one or more
monofunctional monomers are at a level up to about 5 wt %, or about
10 wt %, or about 15 wt % of the sulfur polymer.
In some embodiments, the sulfur polymer is a thermoplastic or a
thermoset. The sulfur polymer may be used in preparing elastomers,
resins, lubricants, coatings, antioxidants, cathode materials for
electrochemical cells, and dental adhesives/restorations. For
example, the sulfur polymer may be formed into a polymeric
film.
According to yet another embodiment of the present invention, a
method of synthesizing a high molecular weight and functional
sulfur polymer is provided. The method may comprise providing about
10-95 wt % of elemental sulfur; adding about 5-50 wt % of
non-homopolymerizing monomers to the elemental sulfur, wherein the
non-homopolymerizing monomers are capable of copolymerizing with
the elemental sulfur; heating the elemental sulfur and
non-homopolymerizing monomers mixture to initiate copolymerization;
and copolymerizing the elemental sulfur and the
non-homopolymerizing monomers via free radical polymerization,
thereby forming the sulfur polymer. The method can be effective for
synthesizing a functional sulfur polymer having a molar mass of at
least 2,000 g/mole.
In one embodiment, the method may further comprise pre-heating the
elemental sulfur to form a molten sulfur, prior to adding the
non-homopolymerizing monomers. The elemental sulfur can be heated
to a temperature of about 120 to 130.degree. C. in order to form
sulfur radicals that copolymerize with the non-homopolymerizing
monomers.
In some embodiments, the elemental sulfur and non-homopolymerizing
monomers are heated to a temperature of about 120 to 230.degree. C.
Heating the elemental sulfur allows for formation of sulfur
radicals that can copolymerize with the non-homopolymerizing
monomers via free radical polymerization. For example, the
non-homopolymerizing monomers react with the sulfur radicals via a
thiol-ene reaction or other related processes.
In some embodiments, the non-homopolymerizing monomers are
ethylenically unsaturated monomers. Non-limiting examples of these
non-homopolymerizing, ethylenically unsaturated monomers include
maleimide monomers, norbornene monomers, allylic monomers, monomers
having at least one vinyl ether moiety, and monomers having at
least one isopropenyl moiety.
In some embodiments, the present invention features another method
of synthesizing a high molecular weight and functional sulfur
polymer. The method may comprise providing about 10-95 wt % of
sulfur copolymers; adding about 5-50 wt % of non-homopolymerizing
monomers to the sulfur copolymers, wherein the non-homopolymerizing
monomers are capable of copolymerizing with the sulfur copolymers;
heating the sulfur copolymers and non-homopolymerizing monomers
mixture to initiate copolymerization; and copolymerizing the sulfur
copolymers and the non-homopolymerizing monomers via free radical
polymerization, thereby forming the sulfur polymer. Preferably, the
method is effective for synthesizing a functional sulfur polymer
having a molar mass of at least 2,000 g/mole.
In one embodiment, the sulfur copolymers may comprise sulfur
monomers at about 10-95 wt % of the sulfur copolymers, and one or
more comonomers at about 5-50 wt % of the sulfur copolymers. The
comonomers may be selected from a group consisting of amine
comonomers, thiol comonomers, sulfide comonomers, alkynylly
unsaturated comonomers, epoxide comonomers, nitrone comonomers,
aldehyde comonomers, ketone comonomers, thiirane comonomers,
ethylenically unsaturated comonomers, styrenic comonomers, vinylic
comonomers, methacrylate comonomers, and acrylonitrile
comonomer.
In an exemplary embodiment, the sulfur copolymer is prepared by the
copolymerization of the one or more comonomers with the sulfur
monomers. For example, elemental sulfur is heated to form sulfur
radicals, the comonomers are added to the sulfur radicals, and the
comonomers can polymerize with the sulfur radicals to form the
sulfur copolymer.
In one embodiment, the non-homopolymerizing monomers may be
ethylenically unsaturated monomers, such as maleimide monomers,
norbornene monomers, allylic monomers, monomers having at least one
vinyl ether moiety, and monomers having at least one isopropenyl
moiety.
In another embodiment, the method of synthesizing the sulfur
polymer may further comprise pre-heating the sulfur copolymer to
form a liquid copolymer, prior to adding the non-homopolymerizing
monomers. For example, the sulfur copolymer may be heated to a
temperature of about 120 to 230.degree. C. in order to form sulfur
copolymer radicals that copolymerize with the non-homopolymerizing
monomers.
In yet another embodiment, the sulfur copolymers and
non-homopolymerizing monomers may be heated to a temperature of
about 120 to 230.degree. C. Heating this mixture allows for the
formation of sulfur copolymer radicals that can copolymerize with
the non-homopolymerizing monomers. For instance, the
non-homopolymerizing monomers can react with the sulfur copolymer
radicals via a thiol-ene reaction or other related processes.
According to alternative embodiments, the methods of synthesizing
the sulfur polymer described herein may be performed in a solvent.
The solvent may comprise an organic solvent, such as aromatic
solvent.
In still other embodiments, the methods of synthesizing the sulfur
polymer described herein may further comprise reacting an available
reactive functional group of the functional sulfur polymer with one
or more comonomers to form a sulfur terpolymer. The technique of
reacting can be oxidative coupling, free radical polymerization, or
copolymerization.
In some embodiments, the one or more comonomers are about 5-50 wt %
of the sulfur terpolymer. In other embodiments, the one or more
comonomers are about 5 about 5 to 10 wt %, or about 10 to 20 wt %,
or about 20 to 30 wt %, or about 30 to 40 wt %, or about 40 to 50
wt % of the sulfur terpolymer. These comonomers may be a vinyl
monomer, an isopropenyl monomer, an acryl monomer, a methacryl
monomer, an unsaturated hydrocarbon monomer, an epoxide monomer, a
thiirane monomer, an alkynyl monomer, a diene monomer, a butadiene
monomer, an isoprene monomer, a norbornene monomer, an amine
monomer, a thiol monomer, a sulfide monomer, an alkynylly
unsaturated monomer, a nitrone monomer, an aldehyde monomer, a
ketone monomer, an ethylenically unsaturated monomer, or a styrenic
monomer.
In other embodiments, the one or more comonomers may be a polyvinyl
monomer, a polyisopropenyl monomer, a polyacryl monomer, a
polymethacryl monomer, a polyunsaturated hydrocarbon monomer, a
polyepoxide monomer, a polythiirane monomer, a polyalkynyl monomer,
a polydiene monomer, a polybutadiene monomer, a polyisoprene
monomer, a polynorbornene monomer, a polyamine monomer, a polythiol
monomer, a polysulfide monomer, a polyalkynylly unsaturated
monomer, a polynitrone monomer, a polyaldehyde monomer, a
polyketone monomer, or a polyethylenically unsaturated monomer.
Examples of techniques of polymerizing include, but are not limited
to, free radical polymerization, controlled radical polymerization,
ring-opening polymerization, ring-opening metathesis
polymerization, step-growth polymerization, and chain-growth
polymerization. When polymerizing the elemental sulfur or sulfur
copolymers with the non-homopolymerizing monomers, at least one
functional sulfur moiety of the elemental sulfur or sulfur
copolymers bonds with at least one functional moiety, i.e. the
alkene moiety, of the non-homopolymerizing monomers.
For illustrative purposes, the following are non-limiting examples
of preparing a sulfur polymer, namely, with non-conventional
comonomers.
Example 3. Synthesis of Methyl 4-(Allyloxy)Benzoate
To a 250 mL round bottom flask was added 8.83 g (58.04 mmol) of
methyl-4-hydroxybenzoate, 9.81 g (70.98 mmol) of potassium
carbonate, 0.78 g (2.95 mmol) of 18-crown-6, 6.2 mL (71.64 mmol) of
allyl bromide and 50 mL of acetone and the reaction mixture was
refluxed overnight. The reaction mixture was gravity filtered and
acetone was removed by rot-vap. Then the crude product was
dissolved in DCM and washed with 1M NaOH, 1M NaHSO.sub.4, brine and
dried with Na.sub.2SO.sub.4. DCM was removed by rot-yap and 5.8 g
of colorless liquid was collected (52% yield).
Example 4. Synthesis of Methyl 3,5-Bis(Allyloxy)Benzoate
To a 100 mL round bottom flask was added 0.98 g (5.80 mmol) of
3,5-dihydroxy methyl benzoate, 1.96 g (14.20 mmol) of potassium
carbonate, 0.156 g (0.59 mmol) of 18-crown-6, 1.24 mL (14.33 mmol)
and 30 mL acetone and the reaction mixture was refluxed overnight.
The reaction mixture was gravity filtered and acetone was removed
by rot-yap. Then the crude product was dissolved in DCM and washed
with 1M NaOH, 1M NaHSO.sub.4, brine and dried with
Na.sub.2SO.sub.4. DCM was removed by rot-yap and 0.64 g of white
solid was collected (44% yield).
Example 5. Sulfur-methyl 4-(allyloxy)benzoate Copolymerization
To a 5 mL glass vial equipped a magnetic stir bar was added 700 mg
(2.73 mmol) of elemental sulfur and 300 mg (1.56 mmol) of methyl
4-(allyloxy)benzoate and the reaction mixture was heated to
170.degree. C. The reaction mixture was not miscible at the
beginning but became red, homogenous solution after 40 min. The
complete consumption of 4-(allyloxy)benzoate was confirmed by 1H
NMR spectra after 2 h yielding a dark brown fluid. The product
turned opaque when cooling to room temperature. The crude product
was dissolved in CS.sub.2 and loaded on the silica column. The
unreacted sulfur was eluted by hexanes (R.sub.f=0.8, SiO.sub.2,
hexanes) and the polymer was eluted by THF (60% yield).
Example 6. Sulfur-methyl 3,5-bis(allyloxy)benzoate
Copolymerization
To a 5 mL glass vial equipped a magnetic stir bar was added 900 mg
(3.52 mmol) of elemental sulfur and 100 mg (0.40 mmol) of
Sulfur-methyl 3,5-bis(allyloxy)benzoate and the reaction mixture
was heated to 170.degree. C. The reaction mixture was not miscible
at the beginning but became red, homogenous solution after 40 min.
The complete consumption of methyl 3,5-bis(allyloxy)benzoate was
confirmed by 1H NMR spectra after 1.5 yielding a dark red robber.
The product is insoluble in common organic solvents
(CH.sub.2Cl.sub.2, CHCl.sub.3, THF and CS.sub.2).
Example 7. Sulfur-methyl 3,5-bis(allyloxy) benzoate-methyl
4-(allyloxy) benzoate Copolymerization
To a 5 mL glass vial equipped a magnetic stir bar was added 350 mg
(1.37 mmol) of elemental sulfur and 100 mg (0.52 mmol) of methyl
4-(allyloxy)benzoate and 50 mg (0.20 mmol) of methyl
3,5-bis(allyloxy)benzoate and the reaction mixture was heated to
170.degree. C. The reaction mixture became red, homogenous solution
after 40 min and vitrified after 50 min. The complete consumption
of methyl 4-(allyloxy)benzoate and methyl 3,5-bis(allyloxy)benzoate
was confirmed by 1H NMR spectra after 3 h yielding a dark brown
solid. The crude product was dissolved in CS.sub.2 and loaded on
the silica column. The unreacted sulfur was eluted by hexanes
(R.sub.f=0.8, SiO.sub.2, hexanes) and the polymer was eluted by THF
(68% yield).
Example 8. Sulfur-2,4,6-Triallyloxy-1,3,5-triazine
Copolymerization
To a 5 mL glass vial equipped a magnetic stir bar was added 900 mg
(3.52 mmol) of elemental sulfur and 100 mg (0.40 mmol) of
2,4,6-Triallyloxy-1,3,5-triazine and the reaction mixture was
heated to 170.degree. C. 0.6 mL of 1,2-dichlorobenzene was used to
dissolve the reagents. The reaction system turned red after 25 min
and orange precipitate formed after 1 h. The complete consumption
of 2,4,6-Triallyloxy-1,3,5-triazine was confirmed by NMR after 1 h.
The reaction mixture was centrifuged and washed with methanol. 703
mg orange powder was isolated (yield 70%) and the product is
insoluble in common organic solvents (CH.sub.2Cl.sub.2, CHCl.sub.3,
THF and CS.sub.2).
Nucleophilic Activators
Referring now to FIG. 14-16, an embodiment of the present invention
features a method of synthesizing a sulfur copolymer comprising
providing about 20-95 mol % of elemental sulfur, heating the
elemental sulfur to form a liquid sulfur, adding about 0.1-10 mol %
of a nucleophilic activator to the liquid sulfur to form an
activated sulfur intermediate, adding about 5-90 mol % of one or
more comonomers to the activated sulfur intermediate, and
polymerizing the one or more comonomers with the activated sulfur
intermediate to form the sulfur copolymer. The step of polymerizing
the comonomers with the activated linear polysulfide intermediate
can occur at a temperature below about 130.degree. C., for example,
below about 120.degree. C. In some embodiments, the nucleophilic
activator can catalyze ring-opening of the liquid sulfur via
nucleophilic activation, thereby forming the activated sulfur
intermediate. Preferably, the nucleophilic activator enables
formation of a homogeneous mixture of the comonomers and the
activated sulfur intermediate such that the comonomers are miscible
with the activated sulfur intermediate. As known to one of ordinary
skill in the art, the term "miscible" is defined as an ability of
substances to mix in all proportions, thereby forming a homogeneous
solution.
Preferably, the elemental sulfur is heated to a temperature of
about 120 to 140.degree. C. For instance, the elemental sulfur is
heated to a temperature of about 130.degree. C. to form the liquid
sulfur. In some embodiments, this temperature range allows
homolytical cleaving of S--S bonds in the activated sulfur
intermediate to generate sulfur radicals for copolymerization with
the comonomers. In other embodiments, the activated sulfur
intermediate is further cooled to a temperature below about
120.degree. C. prior to adding to the comonomers.
In one embodiment, a technique of polymerizing can be free radical
polymerization. As an example of free radical polymerization, the
nucleophilic activator can lower the bond dissociation energy (BDE)
of an S--S bond of the activated sulfur intermediate. The S--S bond
can spontaneously break to form initiating sulfur radicals that can
polymerize with the one or more comonomers. As shown in FIG. 16,
reaction (c) demonstrates an example of free radical
polymerization. In another embodiment, a technique of polymerizing
can be electrophilic substitution. As an example of electrophilic
substitution, such as, the electrophilic aromatic substitution of
reaction (c) in FIG. 16, the one or more comonomers can bond to the
activated sulfur intermediate. The activated sulfur intermediate
may be a sulfobetaine intermediate.
In some embodiments, the elemental sulfur are between about 20 to
30 mol %, 30 to 40 mol %, 40 to 60 mol %, 60 to 80 mol %, or 80 to
95 mol %. For example, the elemental sulfur is at least about 50
mol %. In other embodiments, the one or more comonomers are between
about 5 to 20 mol %, 20 to 40 mol %, 40 to 60 mol %, 60 to 80 mol
%, or 80 to 90 mol %. In further embodiments, the nucleophilic
activator is between about 0.1 to 2 mol %, 2 to 4 mol %, 4 to 6 mol
%, 6 to 8 mol %, or 8 to 10 mol %.
The choice of nucleophilic activator may be determined according to
its ability to reduce the BDE in the S--S bond and to achieve a
desired reactivity in the homolytical cleavage of the S--S bonds.
Non-limiting examples of the nucleophilic activator may include,
but are not limited to amine-containing compounds,
nitrogen-containing heterocycles, nucleophilic heterocycles,
sulfide-containing compounds, imidazoles, functional imidazoles,
anilines, aminostyrene derivatives,
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),
1,4-diazabicyclo[2.2.2]octane (DABCO), N-heterocyclic carbenes,
phosphines, ionic liquids, thiols, ureas, or nucleophilic
organocatalysts.
In some embodiments, the one or more comonomers is selected from a
group consisting of amine comonomers, thiol comonomers, sulfide
comonomers, alkynylly unsaturated comonomers, epoxide comonomers,
nitrone comonomers, aldehyde comonomers, ketone comonomers,
thiirane comonomers, ethylenically unsaturated comonomers, or
styrenic comonomers. In other embodiments, the nucleophilic
activator and the one or more comonomers are identical. For
instance, the nucleophilic activator and the one or more comonomers
are the same compound, such as phenylenediamine (PDA). The one or
more comonomers may contain at least one functional moiety that can
copolymerize with sulfur or the activated sulfur intermediate.
In some embodiments, the sulfur copolymer may have one or more
available reactive functional groups disposed on the one or more
comonomers. The one or more comonomers may be bonded to the
activated sulfur intermediate via a primary functional group of the
comonomer. The comonomer may have a secondary functional group,
i.e. the available reactive functional group, which is not bonded
to the activated sulfur intermediate.
In other embodiments, the one or more comonomers may be styrenic
comonomers. The styrenic comonomers may comprise a vinyl moiety and
one or more available reactive functional groups. The vinyl moiety
can bonded to the initiating sulfur radical to form a sulfur
copolymer. In one embodiment, the one or more available reactive
functional groups are selected from a group consisting of a halogen
functional group, an amine functional group, an alkyl functional
group, an alkyl halide functional group, an alkoxyl functional
group, a phenyl functional group, or a nitro functional group. In
another embodiment, the one or more available reactive functional
groups are selected from a group consisting of carboxylic acids,
carboxylate salts, sulfonic acids, sulfonate salts, quaternary
ammonium salts, ethers, oligo-ethers, polyethers, polyamines,
esters, amides, or alcohols. For example, the halogen functional
group is selected from a group consisting of Br, Cl, and F. The
alkyl halide functional group may comprise one or more moieties of
Br, Cl, or F. In other embodiments, the functional group comprises
--OCH.sub.3, --COOH, or --COOR.
In other embodiments, the method may further comprise removing the
nucleophilic activator from the sulfur copolymer. The nucleophilic
activator may be removed by washing or rinsing away from the sulfur
copolymer.
In still other embodiments, the method may further comprise
reacting the available reactive functional group of the sulfur
copolymer with one or more termonomers. The technique of reacting
may be oxidative coupling, polymerization, or copolymerization. In
one embodiment, the one or more termonomers may be a vinyl monomer,
an isopropenyl monomer, an acryl monomer, a methacryl monomer, an
unsaturated hydrocarbon monomer, an epoxide monomer, a thiirane
monomer, an alkynyl monomer, a diene monomer, a butadiene monomer,
an isoprene monomer, a norbornene monomer, an amine monomer, a
thiol monomer, a sulfide monomer, an alkynylly unsaturated monomer,
a nitrone monomer, an aldehyde monomer, a ketone monomer, an
ethylenically unsaturated monomer, a or a styrenic monomer. In
another embodiment, the one or more termonomers may be a group
consisting of a polyvinyl monomer, a polyisopropenyl monomer, a
polyacryl monomer, a polymethacryl monomer, a polyunsaturated
hydrocarbon monomer, a polyepoxide monomer, a polythiirane monomer,
a polyalkynyl monomer, a polydiene monomer, a polybutadiene
monomer, a polyisoprene monomer, a polynorbornene monomer, a
polyamine monomer, a polythiol monomer, a polysulfide monomer, a
polyalkynylly unsaturated monomer, a polynitrone monomer, a
polyaldehyde monomer, a polyketone monomer, a polyethylenically
unsaturated monomer, or a polystyrenic monomer.
In some embodiments, the method of synthesizing the sulfur
copolymer may be performed in a solution. For example, the solution
may be an aqueous medium or an organic solvent, such as toluene,
THF, DMSO, and DMF. Preferably, synthesis of the sulfur copolymer
may be performed in a solution for styrene-containing
comonomers.
In one embodiment, the sulfur copolymers may comprise dynamic
sulfur-sulfur (S--S) bonds. Preferably, when the dynamic S--S bonds
of the sulfur copolymer are broken, the S--S bonds are reconnected
by thermal reforming.
In some embodiments, the sulfur copolymer may be a thermoplastic or
a thermoset for use in elastomers, resins, lubricants, coatings,
antioxidants, cathode materials for electrochemical cells, dental
adhesives/restorations. For example, the sulfur copolymer may be a
thermoplastic rubber or a thermoplastic elastomer. In another
embodiment, the sulfur copolymer may be in a form of a polymeric
film. For example, the sulfur copolymer may be a thin film coating
for a surface of a substrate.
Another embodiment of the present invention features a sulfur
polymer comprising about 20-95 mol % of elemental sulfur, about
0.1-10 mol % of a nucleophilic activator, and about 5-90 mol % of
one or more comonomers. Preferably, the nucleophilic activator
reacts with the elemental sulfur to ring open the elemental sulfur
via nucleophilic activation to form an activated sulfur
intermediate prior to polymerizing with the one or more monomers,
wherein the nucleophilic activator enables formation of a
homogeneous mixture of the comonomers and the activated sulfur
intermediate such that the comonomers are miscible with the
activated sulfur intermediate.
Non-limiting examples of the nucleophilic activator may include,
but are not limited to amine-containing compounds,
nitrogen-containing heterocycles, nucleophilic heterocycles,
sulfide-containing compounds, imidazoles, functional imidazoles,
anilines, aminostyrene derivatives,
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),
1,4-diazabicyclo[2.2.2]octane (DABCO), N-heterocyclic carbenes,
phosphines, ionic liquids, thiols, ureas, and nucleophilic
organocatalysts.
In some embodiments, the one or more comonomers may be amine
comonomers, thiol comonomers, sulfide comonomers, alkynylly
unsaturated comonomers, epoxide comonomers, nitrone comonomers,
aldehyde comonomers, ketone comonomers, thiirane comonomers,
ethylenically unsaturated comonomers, or styrenic comonomers. In
other embodiments, the sulfur polymer may have one or more
available reactive functional groups disposed on the one or more
comonomers, with the provision that the one or more available
reactive functional groups is not directly linked to the sulfur. In
still other embodiments, the nucleophilic activator and the one or
more comonomers are identical, i.e. the same compound.
In some embodiments, the styrenic comonomers may comprise a vinyl
moiety and one or more available reactive functional groups. The
vinyl functional group of the styrenic comonomers can react with
the activated sulfur intermediate to form the sulfur copolymer
having the one or more available reactive functional groups. In one
embodiment, the one or more available reactive functional groups
may comprise a halogen functional group, an amine functional group,
an alkyl functional group, an alkyl halide functional group, an
alkoxyl functional group, a phenyl functional group, or a nitro
functional group. In another embodiment, the one or more available
reactive functional groups may be carboxylic acids, carboxylate
salts, sulfonic acids, sulfonate salts, quaternary ammonium salts,
ethers, oligo-ethers, polyethers, polyamines, esters, amides, or
alcohols. For example, the halogen functional group or the may be a
Br, Cl, and F. As another example, the alkyl halide functional
group may comprise one or more moieties of Br, Cl, or F. In other
embodiments, the functional group comprises --OCH.sub.3, --COOH, or
--COOR.
In other embodiments, the sulfur polymer may further comprise about
5 to 50 mol % of one or more termonomers. Each termonomer may be
linked to the available reactive functional group disposed on the
one or more comonomers. In one embodiment, the one or more
termonomers may be a vinyl monomer, an isopropenyl monomer, an
acryl monomer, a methacryl monomer, an unsaturated hydrocarbon
monomer, an epoxide monomer, a thiirane monomer, an alkynyl
monomer, a diene monomer, a butadiene monomer, an isoprene monomer,
a norbornene monomer, an amine monomer, a thiol monomer, a sulfide
monomer, an alkynylly unsaturated monomer, a nitrone monomer, an
aldehyde monomer, a ketone monomer, an ethylenically unsaturated
monomer, or a styrenic monomer. In another embodiment, the one or
more termonomers are selected from a group consisting of a
polyvinyl monomer, a polyisopropenyl monomer, a polyacryl monomer,
a polymethacryl monomer, a polyunsaturated hydrocarbon monomer, a
polyepoxide monomer, a polythiirane monomer, a polyalkynyl monomer,
a polydiene monomer, a polybutadiene monomer, a polyisoprene
monomer, a polynorbornene monomer, a polyamine monomer, a polythiol
monomer, a polysulfide monomer, a polyalkynylly unsaturated
monomer, a polynitrone monomer, a polyaldehyde monomer, a
polyketone monomer, a polyethylenically unsaturated monomer, or a
polystyrenic monomer.
In some embodiments, the sulfur polymer may further comprise a
solution. For example, the elemental sulfur, the nucleophilic
activator, and the one or more comonomers may be disposed in the
solution. The solution may be an aqueous medium or an organic
solvent such as toluene, THF, DMSO, and DMF.
Another embodiment of the present invention features a method of
making an article formed from any of the sulfur polymers described
herein. In some embodiments, the method may comprise heating the
sulfur polymer to a temperature in the range of about 120.degree.
C. to about 230.degree. C. to form a prepolymer, forming the
prepolymer into a shape of the article to yield a formed
prepolymer, and curing the formed prepolymer to yield the article.
In one embodiment, the prepolymer is coated and cured as a thin
film on a substrate. In another embodiment, the prepolymer is
shaped and cured using a mold.
Further embodiments of the present invention features an
electrochemical cell comprising an anode comprising metallic
lithium, a cathode comprising any of the sulfur polymer described
herein, and a non-aqueous electrolyte interposed between the
cathode and the anode. In some embodiments, the electrochemical
cell may have an increased volumetric energy density. In other
embodiments, a capacity of the electrochemical cell ranges from
about 200 to about 1500 mAh/g.
In still other embodiments, the present invention may feature an
optical substrate comprising any of the sulfur polymer described
herein. The optical substrate may be a substantially transparent
optical body, such as a film, a lens, or a free-standing object. In
some embodiments, the optical substrate has a refractive index in
the range of about 1.7 to about 2.6 and at least one wavelength in
the range of about 500 nm to about 10 .mu.m. Preferably, the
optical substrate has an optical transparency in the visible and
infrared spectrum.
Experimental
The following are exemplary and non-limiting embodiments of
copolymerizing elemental sulfur with a comonomer using a
nucleophilic activator.
Example 9. Copolymerization of Sulfur and 4-vinylaniline
Elemental sulfur (S.sub.8) was added to a glass vial equipped with
a magnetic stir bar and heated to about 120-130.degree. C. until
liquid sulfur was formed. A 4-vinylaniline was added dropwise to
the liquid sulfur. The reaction mixture was heated for about 20-30
minutes until no 4-vinylaniline monomers remained.
Example 10. Copolymerization of Sulfur and Styrene
Polymerizing of liquid sulfur and styrene (at T.apprxeq.120.degree.
C.) in the presence of about 1-10 mol % of a nucleophilic activator
that can ring-open S.sub.8 to form sulfobetaine intermediates
resulted in a 2-100 fold rate acceleration.
Example 11
S.sub.8 was added to a glass vial equipped with a magnetic stir bar
and heated to 130.degree. C. until liquid sulfur was formed.
Styrene and about 1 mol % of 1-methylimidazole was added to the
liquid sulfur. The reaction mixture was heated at 120.degree. C.
for about 2.5 hours until no styrene monomers remained.
Another embodiment of the present invention features a method of
solubilizing elemental sulfur (S.sub.8) in a reactive media. The
method may comprise providing about 5-99 mol % of elemental sulfur,
heating the elemental sulfur to form a liquid sulfur, adding about
0.1-10 mol % of a nucleophilic activator to the liquid sulfur,
wherein the nucleophilic activator promotes ring-opening of the
liquid sulfur via nucleophilic activation, thereby forming an
activated linear polysulfide intermediate, and adding the activated
linear polysulfide intermediate to the reactive media thereby
forming a homogeneous reaction mixture. Preferably, the activated
linear polysulfide intermediate is soluble in the reactive media at
a temperature below about 120.degree. C. As used herein, the term
"solubilize", and derivatives thereof, are defined as forming
homogeneous reaction mixtures, which is characterized by the
formation of transparent fluid phases.
In yet another embodiment, the present invention may feature a
sulfur copolymer prepared by a process comprising the steps of
providing about 5-99 mol % of elemental sulfur, heating the
elemental sulfur to form a liquid sulfur, adding about 0.1-10 mol %
of a nucleophilic activator to the liquid sulfur, wherein the
nucleophilic activator promotes ring-opening of the liquid sulfur
via nucleophilic activation, thereby forming an activated linear
polysulfide intermediate, adding about 5-50 mol % of one or more
comonomers to the activated linear polysulfide intermediate,
wherein the nucleophilic activator enables formation of a
homogeneous mixture of the comonomers and the activated linear
polysulfide intermediate such that the comonomers are miscible with
the activated linear polysulfide intermediate, and polymerizing the
one or more comonomers with the activated linear polysulfide
intermediate to form a sulfur copolymer, wherein polymerizing the
comonomers with the activated linear polysulfide intermediate
occurs at a temperature below about 120.degree. C. In a further
embodiment, the process may further comprise adding the activated
linear polysulfide intermediate to a reactive media prior to adding
the comonomers, thereby forming a homogeneous reaction mixture
wherein the activated linear polysulfide compound is soluble in the
reactive media at a temperature below about 120.degree. C. In yet
another embodiment, the process further comprises reacting the
available reactive functional group of the sulfur copolymer with
one or more termonomers.
In some embodiments, the nucleophilic activator is selected from a
group consisting of amine-containing compounds, nitrogen-containing
heterocycles, sulfide-containing compounds, imidazoles, functional
imidazoles, anilines, aminostyrene derivatives,
1,8-diazabicyclo[5.4.0.]undec-7-ene (DBU),
1,4-diazabicyclo[2.2.2]octane (DABCO), nucleophilic heterocycles,
N-heterocyclic carbenes, phosphines, aromatic phosphines, ionic
liquids, thiols, ureas, and nucleophilic organocatalysts.
Preferably, the nature of the nucleophilic activator can be used to
tune the solubility of the elemental sulfur with the activator, or
with other comonomers in presence of sulfur and nucleophilic
activator. Hence, use of nucleophilic activators with substituents
may be used or designed to modify the solubility, or miscibility of
activated sulfur intermediates into polar or nonpolar reactive
media, such as solvents or comonomers that are unsaturated or
vinylic substances that can copolymerize with elemental sulfur.
In one embodiment, the reactive media may comprise an organic
solvent, such as toluene, THF, DMSO, and DMF, a diluent, an aqueous
medium, or a combination thereof. One or more comonomers may be
added to the homogenous reaction mixture and polymerize with the
activated linear polysulfide intermediate to form a sulfur
copolymer. In another embodiment, the reactive media may comprise
one or more comonomers, which can polymerize with the activated
linear polysulfide intermediate to form a sulfur copolymer.
In some embodiments, the elemental sulfur, the nucleophilic
activator and the reactive media can be initially premixed prior to
heating. In other embodiments, the elemental sulfur, the
nucleophilic activator and the comonomers can be initially premixed
prior to heating. In still other embodiments, the elemental sulfur,
the nucleophilic activator, the comonomers, and the reactive media
can be initially premixed prior to heating. Initiators, such as
conventional azo or peroxide initiators, may also be added in any
of the premixed compositions.
In some embodiments, a technique of polymerizing is free radical
polymerization, wherein the nucleophilic activator lowers a bond
dissociation energy of an S--S bond of the polysulfide
intermediate, wherein spontaneous breaking of the S--S bond forms
initiating sulfur radicals that polymerize with the one or more
comonomers. The nucleophilic activator and elemental sulfur enable
a neat mixture, or a mixture diluted in a solvent to temperatures
less than, or equal to the melting point of sulfur, with the
addition of an initiator, catalyst, or other mediator that can
promote free radical copolymerization. In other embodiments, the
technique of polymerizing is electrophilic substitution, wherein
the one or more comonomers bond to the activated polysulfide
intermediate. In further embodiments, an initiator may be added to
the reaction mixture to initiate and enhance rate of polymerization
of the one or more comonomers and the activated linear polysulfide
intermediate.
In one embodiment, the one or more comonomers is selected from a
group consisting of amine comonomers, thiol comonomers, sulfide
comonomers, alkynylly unsaturated comonomers, epoxide comonomers,
nitrone comonomers, aldehyde comonomers, ketone comonomers,
thiirane comonomers, ethylenically unsaturated comonomers, styrenic
comonomers, vinylic comonomers, methacrylate comonomers, and
acrylonitrile comonomers. Other examples of comonomers include, but
are not limited to, DIB and analogues, alkynes, alkenes,
unsaturated, cyclic saturated, aliphatic compounds with
unsaturation, methacrylates, acrylates, dienes, polydienes,
acrylonitrile, vinyl ethers, vinyl esters and functional vinylic
comonomers. In still other embodiments, the ethylenically
unsaturated comonomers are comonomers that are capable of
thiol-ene, or thiol-yne reactions.
Preferably, the nucleophilic activator upon reaction with liquid
sulfur renders the mixture soluble at temperatures lower than
120.degree. C. (which is the melting point of sulfur) in
conventional vinylic or unsaturated comonomers, which includes
those from the family of styrenics, acrylates, methacrylates,
acrylonitrile, vinyl esters, vinyl ethers, dienes, polyenes, cyclic
unsaturated compounds. Without wishing to limit the invention to a
particular theory or mechanism, the limited solubility of elemental
sulfur in conventional comonomers or solvents, and the limited
miscibility of liquid sulfur in the same can be resolved by the
nucleophilic activators. For volatile comonomers with low
miscibility in liquid sulfur, these methods enable for the first
time a route to form homogeneous mixtures suitable for free radical
copolymerization reactions.
In one embodiment, the elemental sulfur is heated to a temperature
of about 120.degree. C., i.e. the melting point of elemental
sulfur. In another embodiment, the elemental sulfur is heated to a
temperature of about 120-130.degree. C. In one referred embodiment,
the activated linear polysulfide intermediate is cooled to a
temperature below about 120.degree. C. prior to adding to the
reactive media. For instance, the polysulfide intermediate may be
cooled to about 70-115.degree. C. As another example, the
polysulfide intermediate may be cooled to about or below the
boiling point of the comonomers.
In some embodiments, the sulfur copolymer has one or more available
reactive functional groups disposed on the one or more comonomers.
The one or more available reactive functional groups can be a
halogen functional group, such as Br, Cl, and F, an amine
functional group, an alkyl functional group, an alkyl halide
functional group, which may comprise one or more moieties of Br,
Cl, or F, an alkoxyl functional group, a phenyl functional group, a
nitro functional group, carboxylic acids (COOH), carboxylate salts,
sulfonic acids, sulfonate salts, quaternary ammonium salts, ethers
(--OCH.sub.3), oligo-ethers, polyethers, polyamines, esters
(--COOR), amides, or alcohols.
In other embodiments, the nucleophilic activator and the one or
more comonomers are identical. The one or more comonomers may have
a functional moiety that copolymerizes with the activated
polysulfide intermediate. In alternate embodiments, the
nucleophilic activator is removed, i.e. washed away, from the
sulfur copolymer.
According to some embodiments, the available reactive functional
group of the sulfur copolymer may be reacted with one or more
termonomers. A technique of reacting can be oxidative coupling,
polymerization, or copolymerization. Examples of termonomers
include, but are not limited to, a vinyl monomer, an isopropenyl
monomer, an acryl monomer, a methacryl monomer, an unsaturated
hydrocarbon monomer, an epoxide monomer, a thiirane monomer, an
alkynyl monomer, a diene monomer, a butadiene monomer, an isoprene
monomer, a norbornene monomer, an amine monomer, a thiol monomer, a
sulfide monomer, an alkynylly unsaturated monomer, a nitrone
monomer, an aldehyde monomer, a ketone monomer, an ethylenically
unsaturated monomer, or a styrenic monomer. Further examples of the
one or more termonomers include, but are not limited to, a
polyvinyl monomer, a polyisopropenyl monomer, a polyacryl monomer,
a polymethacryl monomer, a polyunsaturated hydrocarbon monomer, a
polyepoxide monomer, a polythiirane monomer, a polyalkynyl monomer,
a polydiene monomer, a polybutadiene monomer, a polyisoprene
monomer, a polynorbornene monomer, a polyamine monomer, a polythiol
monomer, a polysulfide monomer, a polyalkynylly unsaturated
monomer, a polynitrone monomer, a polyaldehyde monomer, a
polyketone monomer, a polyethylenically unsaturated monomer, or a
polystyrenic monomer.
In preferred embodiments, the sulfur copolymer may be a
thermoplastic or a thermoset for use in elastomers, resins,
lubricants, coatings, antioxidants, cathode materials for
electrochemical cells, dental adhesives/restorations.
Another embodiment of the present invention features a method of
making an article formed from any of the sulfur copolymers
described herein. In some embodiments, the method may comprise
heating the sulfur copolymer composition to a temperature in the
range of about 120.degree. C. to about 230.degree. C. to form a
prepolymer, forming the prepolymer into a shape of the article to
yield a formed prepolymer, and curing the formed prepolymer to
yield the article. In one embodiment, the prepolymer is coated and
cured as a thin film on a substrate. In another embodiment, the
prepolymer is shaped and cured using a mold.
In still other embodiments, the present invention may feature an
optical substrate comprising any of the sulfur copolymers described
herein. The optical substrate may be a substantially transparent
optical body, such as a film, a lens, or a free-standing object. In
some embodiments, the optical substrate has a refractive index in
the range of about 1.7 to about 2.6 and at least one wavelength in
the range of about 500 nm to about 10 .mu.m. Preferably, the
optical substrate has an optical transparency in the visible and
infrared spectrum.
Further embodiments of the present invention features an
electrochemical cell comprising an anode comprising metallic
lithium, a cathode comprising any of the sulfur copolymers
described herein, and a non-aqueous electrolyte interposed between
the cathode and the anode. In some embodiments, the electrochemical
cell may have an increased volumetric energy density. In other
embodiments, a capacity of the electrochemical cell ranges from
about 200 to about 1500 mAh/g.
Optical Polymers
Referring now to FIGS. 17-36, the chalcogenide copolymers that are
described herein are the first class of polymeric materials that
exhibit high transparency in the short-wave and mid-IR regimes due
to the presence of largely IR inactive S--S bonds. Furthermore,
since these chalcogenide copolymers are readily melt, or solution
processed, fabrication of free standing films, windows, or lenses
can be easily conducted. Access to these kinds of high quality and
inexpensive lenses are anticipated to open new opportunities in low
cost IR optical devices and technologies including IR thermal
imaging rifle scopes and home monitoring.
According to one embodiment, the present invention features a
chalcogenide copolymer comprising one or more cyclic selenium
sulfide monomers having the formula Se.sub.nS.sub.(8-n); and one or
more comonomers each selected from a group consisting of amine
comonomers, thiol comonomers, sulfide comonomers, alkynylly
unsaturated comonomers, epoxide comonomers, nitrone comonomers,
aldehyde comonomers, ketone comonomers, thiirane comonomers,
ethylenically unsaturated comonomers, styrenic comonomers, vinylic
comonomers, methacrylate comonomers, and acrylonitrile comonomers
at a level in the range of about 5-50 wt % of the chalcogenide
copolymer. Assuming that n=7, i.e. Se.sub.7S, then the cyclic
selenium sulfide monomers may comprise at most about 70 wt % of
selenium. In preferred embodiments, the chalcogenide copolymer has
a refractive index of about 1.7-2.6 at a wavelength in a range of
about 500 nm to about 8 .mu.m. The cyclic selenium sulfide monomers
is polymerized with the comonomers such that at least one
functional sulfur moiety of the selenium-sulfide is bonded to at
least one functional moiety of the one or more monomers.
In some embodiments, n in an integer that can range from 1 to 7.
For example, when n=2, the cyclic selenium sulfide monomers have
the formula Se.sub.2S.sub.6. As another example, when n=3, the
cyclic selenium sulfide monomers have the formula Se.sub.3S.sub.5.
Preferably, the one or more cyclic selenium sulfide monomers can
comprise all possible isomers of a specific formula. In alternative
embodiments, the selenium sulfide monomers can be of the formula
Se.sub.nS.sub.m, wherein n ranges from 1 to 7 and m ranges from 1
to 7, wherein the selenium sulfide monomers are not necessarily
cyclic.
In other embodiments, the chalcogenide copolymer may further
comprise one or more sulfur monomers, comprising elemental sulfur
(S.sub.8), at a level of about 1-60 wt % of the chalcogenide
copolymer. In still other embodiments, the chalcogenide copolymer
may further comprise elemental selenium (e.g., Se.sub.8 or other
allotropes), at a level of about 1-60 wt % of the chalcogenide
copolymer. For instance, the chalcogenide copolymer may comprise
one or more cyclic selenium sulfide monomers, sulfur monomers, and
the one or more comonomers; or the the chalcogenide copolymer may
comprise one or more cyclic selenium sulfide monomers, elemental
selenium, and the one or more comonomers. Further still, the
chalcogenide copolymer may comprise one or more cyclic selenium
sulfide monomers, sulfur monomers, elemental selenium, and the one
or more comonomers.
In some embodiments, the chalcogenide copolymer may comprise
S.sub.8 and elemental selenium, in place of the cyclic selenium
sulfide monomers. Without wishing to limit the invention to a
particular theory or mechanism, the Se--Se bonds of elemental
selenium are broken up in the presence of sulfur radicals generated
by the ring opening of S.sub.8, thereby forming a sulfur-selenium
copolymer. Additional comonomers may be added with the S.sub.8 and
elemental selenium, or thereafter to the sulfur-selenium
copolymer.
In one embodiment, the chalcogenide copolymer comprises one or more
cyclic selenium sulfide monomers at a range of about 1 to 5 wt %,
or about 5 to 10 wt %, or about 10 to 20 wt %, or about 20 to 30 wt
%, or about 30 to 40 wt %, or about 40 to 50 wt %, or about 50 to
60 wt %, or about 60 to 70 wt % of the chalcogenide copolymer. In
another embodiment, the cyclic selenium sulfide monomers may
comprise selenium units of at most about 20 wt %, or at most about
30 wt %, or at most about 40 wt % or at most about 50 wt %, or at
most about 60 wt %, or at most about 70 wt % of the cyclic selenium
sulfur monomers.
In some embodiments, the chalcogenide copolymer comprises one or
more comonomers at a range of about 5 to 10 wt %, or about 10 to 20
wt %, or about 20 to 30 wt %, or about 30 to 40 wt %, or about 40
to 50 wt % of the chalcogenide copolymer. In other embodiments, the
chalcogenide copolymer comprises sulfur monomers at a range of
about 1 to 5 wt %, or about 5 to 10 wt %, or about 10 to 20 wt %,
or about 20 to 30 wt %, or about 30 to 40 wt %, or about 40 to 50
wt % of the chalcogenide copolymer. In further embodiments, the
chalcogenide copolymer comprises elemental selenium at a range of
about 1 to 5 wt %, or about 5 to 10 wt %, or about 10 to 20 wt %,
or about 20 to 30 wt %, or about 30 to 40 wt %, or about 40 to 50
wt % of the chalcogenide copolymer. For instance, the chalcogenide
copolymer may comprise 30 wt % sulfur, 35 wt % cyclic
selenium-sulfide, and 35 wt % 1,3diisopropenyl benzene.
In yet other embodiments, the chalcogenide copolymer may further
comprise one or more termonomers selected from a group consisting
of a vinyl monomer, an isopropenyl monomer, an acryl monomer, a
methacryl monomer, an unsaturated hydrocarbon monomer, an epoxide
monomer, a thiirane monomer, an alkynyl monomer, a diene monomer, a
butadiene monomer, an isoprene monomer, a norbornene monomer, an
amine monomer, a thiol monomer, a sulfide monomer, an alkynylly
unsaturated monomer, a nitrone monomer, an aldehyde monomer, a
ketone monomer, an ethylenically unsaturated monomer, or a styrenic
monomer. The termonomers may be present in an amount ranging from
about 5 to 50 wt % of the chalcogenide copolymer.
In still other embodiments, the chalcogenide copolymer may further
comprise one or more polyfunctional monomers selected from a group
consisting of a polyvinyl monomer, a polyisopropenyl monomer, a
polyacryl monomer, a polymethacryl monomer, a polyunsaturated
hydrocarbon monomer, a polyepoxide monomer, a polythiirane monomer,
a polyalkynyl monomer, a polydiene monomer, a polybutadiene
monomer, a polyisoprene monomer, a polynorbornene monomer, a
polyamine monomer, a polythiol monomer, a polysulfide monomer, a
polyalkynylly unsaturated monomers, a polynitrone monomers, a
polyaldehyde monomers, a polyketone monomers, and a
polyethylenically unsaturated monomers. The polyfunctional monomers
may be present in an amount ranging from about 5 to 50 wt % of the
chalcogenide copolymer.
According to some embodiments, the chalcogenide copolymer is
substantially transparent in an infrared or visible spectrum. For
instance, the chalcogenide copolymer may substantially transparent
in a spectrum having a wavelength range of about 1000-1500 nm, or
1500-3000 nm, or about 3000-5000 nm, or about 5-10 microns.
Preferably, the chalcogenide copolymer can be formed into a
substantially transparent substrate, wherein the transparent
substrate is a film, a lens, or a free-standing object.
According to another embodiment, the present invention features a
method of producing a chalcogenide copolymer, said method
comprising providing cyclic selenium sulfide having the formula
Se.sub.nS.sub.(8-n), wherein the cyclic selenium sulfide monomers
comprises at most about 70 wt % of selenium; heating the cyclic
selenium sulfide to form a liquid selenium sulfide; adding about
5-50 wt % of one or more comonomers to the liquid selenium sulfide,
wherein the one or more monomers is selected from a group
consisting of amine comonomers, thiol comonomers, sulfide
comonomers, alkynylly unsaturated comonomers, epoxide comonomers,
nitrone comonomers, aldehyde comonomers, ketone comonomers,
thiirane comonomers, ethylenically unsaturated comonomers, styrenic
comonomers, vinylic comonomers, methacrylate comonomers, and
acrylonitrile comonomers; and polymerizing the comonomers with the
liquid selenium sulfide to form the chalcogenide copolymer. The
chalcogenide copolymer may be further heated until the chalcogenide
copolymer is substantially vitrified. Preferably, the chalcogenide
can have a refractive index of about 1.7-2.6 at a wavelength in a
range of about 500 nm to about 8 .mu.m.
In some embodiments, n in an integer that can range from 1 to 7.
For example, when n=2, the cyclic selenium sulfide can have the
formula Se.sub.2S.sub.6. As another example, when n=3, the cyclic
selenium sulfide can have the formula Se.sub.3S.sub.5. Preferably,
the cyclic selenium sulfide can comprise all possible isomers of a
specific formula. In alternative embodiments, the selenium sulfide
can be of the formula Se.sub.nS.sub.m, wherein n ranges from 1 to 7
and m ranges from 1 to 7, wherein the selenium sulfide are not
necessarily cyclic.
In other embodiments, the method may further comprise adding about
5-50 wt % of elemental sulfur to the cyclic selenium sulfide prior
to adding the comonomers. In yet other embodiments, the method may
further comprise adding adding about 5-50 wt % of elemental
selenium to the cyclic selenium sulfide prior to adding the
comonomers.
Examples of techniques of polymerizing include, but are not limited
to, free radical polymerization, controlled radical polymerization,
ring-opening polymerization, ring-opening metathesis
polymerization, step-growth polymerization, and chain-growth
polymerization. When polymerizing the comonomers with the liquid
selenium sulfide, at least one functional sulfur moiety of the
selenium sulfide to bond with at least one functional moiety of the
one or more monomers.
In still other embodiments, the method may further comprise
polymerizing the chalcogenide copolymer with one or more
termonomers selected from a group consisting of a vinyl monomer, an
isopropenyl monomer, an acryl monomer, a methacryl monomer, an
unsaturated hydrocarbon monomer, an epoxide monomer, a thiirane
monomer, an alkynyl monomer, a diene monomer, a butadiene monomer,
an isoprene monomer, a norbornene monomer, an amine monomer, a
thiol monomer, a sulfide monomer, an alkynylly unsaturated monomer,
a nitrone monomer, an aldehyde monomer, a ketone monomer, an
ethylenically unsaturated monomer, or a styrenic monomer. The
termonomers may be present in an amount ranging from about 5 to 50
wt % of the chalcogenide copolymer.
In still other embodiments, the method may further comprise
polymerizing the chalcogenide copolymer with one or more
polyfunctional monomers (e.g., difunctional or trifunctional). The
one or more polyfunctional monomers may be selected from a group
consisting of a polyvinyl monomer (e.g., divinyl, trivinyl), a
polyisopropenyl monomer (e.g., diisoprenyl, triisoprenyl), a
polyacryl monomer (e.g., diacryl, triacryl), a polymethacryl
monomer (e.g., dimethacryl, trimethacryl), a polyunsaturated
hydrocarbon monomer (e.g., diunsaturated, triunsaturated), a
polyepoxide monomer (e.g., diepoxide, triepoxide), a polythiirane
monomer (e.g., dithiirane, trithiirane), a polyalkynyl monomer, a
polydiene monomer, a polybutadiene monomer, a polyisoprene monomer,
a polynorbornene monomer, a polyamine monomer, a polythiol monomer,
a polysulfide monomer, a polyalkynylly unsaturated monomers, a
polynitrone monomers, a polyaldehyde monomers, a polyketone
monomers, and a polyethylenically unsaturated monomers. The
polyfunctional monomers may be present in an amount ranging from
about 5 to 50 wt % of the chalcogenide copolymer.
In some embodiments, the one or more polyfunctional monomers is
selected from a group consisting of a divinylbenzene, a
diisopropenylbenzene, an alkylene di(meth)acrylate, a bisphenol A
di(meth)acrylate, a terpene, a carotene, a divinyl (hetero)aromatic
compound and a diisopropenyl (hetero)aromatic compound.
In some embodiments, the one or more polyfunctional monomers are at
a level of about 2 to about 50 wt %, or about 2 to about 10 wt %,
or about 10 to about 20 wt %, or about 20 to about 30 wt %, or
about 30 to about 40 wt %, or about 40 to about 50 wt % of the
chalcogenide copolymer. In some embodiments, the one or more
monofunctional monomers are at a level up to about 5 wt %, or about
10 wt %, or about 15 wt % of the chalcogenide copolymer.
According to some embodiments, the method produces a chalcogenide
copolymer that is substantially transparent in an infrared or
visible spectrum. For instance, the chalcogenide copolymer may
substantially transparent in a spectrum having a wavelength range
of about 1000-1500 nm, or 1500-3000 nm, or about 3000-5000 nm, or
about 5-10 microns. Preferably, the chalcogenide copolymer can be
formed into a substantially transparent substrate, wherein the
transparent substrate is a film, a lens, or a free-standing
object.
For instance, the chalcogenide copolymer is coated on a substrate
and cured as a thin film; or shaped and cured using a mold; or
fabricated into an optical device component, such as a lens or
window, for use as a transmitting material in an infrared imaging
device. The chalcogenide copolymer may be processable via solution
or melt processing methods. In some embodiments, the chalcogenide
copolymer is in the form of a thin film. In other embodiments, the
chalcogenide copolymer is in the form of a three-dimensional solid
having a thickness of at least 1 mm in size.
For illustrative purposes, the following is a non-limiting example
of preparing a chalcogenide copolymer.
Example 12. Representative Procedure for the Synthesis of
Poly(Sulfur-Random-Selenium-Random-(1,3-Diisopropenylbenzene)
To an 11 ml scintillation vial, equipped with a magnetic stir bar,
was loaded with about 1.4 g (70 wt %, 2.0 g scale) Selenium Sulfide
(Se.sub.nS.sub.m; 1.4 g) and about 0.65 mL (30 wt %, 2.0 g scale,
d(DIB)=0.925 g/mL) 1,3-diisopropenylbenzene (DIB). The contents of
the vial were mixed via a vortex for about 3 minutes. The vial was
then lowered into a 180.degree. C. thermostated oil bath (set to
850 rpm) for about 80 minutes. The vial was then removed from the
oil bath and the contents of the vial were poured into a PDMS mold
(located in an 180.degree. C. oven, and preheated for at least one
hour), where it was allowed to cure for about 55 minutes. The mold
was then removed from the oven and allowed to cool to RT.
According to one embodiment, the present invention features an
optical sulfur copolymer comprising one or more sulfur monomers at
a level at least about 50 wt % of the optical sulfur copolymer, and
one or more comonomers selected amine monomers, thiol monomers,
sulfide monomers, alkynylly unsaturated monomers, epoxide monomers,
nitrone monomers, aldehyde monomers, ketone monomers, thiirane
monomers, or ethylenically unsaturated monomers at a level in the
range of about 10 wt % to about 50 wt % of the optical sulfur
copolymer. The optical sulfur copolymer can have a refractive index
of about 1.7-2.6 and at least one wavelength in a range of about
500 nm to about 10 .mu.m.
In another embodiment, the optical sulfur copolymer may comprise
one or more sulfur monomers at a level of about 5-95 wt % of the
optical sulfur copolymer, one or more comonomers at a level in the
range of about 1-50 wt % of the optical sulfur copolymer, and one
or more selenium comonomers at a level of about 10-90 wt % of the
optical sulfur copolymer. In some embodiments, at least one
functional sulfur moiety of the one or more sulfur monomers is
bonded to at least one functional moiety of the one or more
monomers. The one or more comonomers may be selected from amine
monomers, thiol monomers, sulfide monomers, alkynylly unsaturated
monomers, epoxide monomers, nitrone monomers, aldehyde monomers,
ketone monomers, thiirane monomers, or ethylenically unsaturated
monomers. In other embodiments, the selenium comonomers are derived
from cyclic selenium sulfide, elemental selenium, or a combination
thereof. The optical sulfur copolymer can have a refractive index
of about 1.7-2.6 and at least one wavelength in a range of about
500 nm to about 10 .mu.m.
In some embodiments, the one or more sulfur monomers is at a level
at least about 60 wt % of the optical sulfur copolymer, or at least
about 70 wt % of the optical sulfur copolymer, or at least about 80
wt % of the optical sulfur copolymer, or at least about 90 wt % of
the optical sulfur copolymer. In other embodiments, the one or more
co monomers is at a level of about 1-15 wt % of the optical sulfur
copolymer, or about 15-30 wt % of the optical sulfur copolymer, or
about 30-40 wt % of the optical sulfur copolymer, or about 40-50 wt
% of the optical sulfur copolymer. For example, the one or more
monomers may be ethylenically unsaturated monomers, such as
diisopropenylbenzene monomers. The diisopropenylbenzene monomers
may be 1,3-diisopropenylbenzene monomers. In further embodiments,
the selenium comonomers are at a level of about 10-20 wt % of the
optical sulfur copolymer, or about 20-40 wt % of the optical sulfur
copolymer, or about 40-60 wt % of the optical sulfur copolymer, or
about 60-80 wt %, or about 80-90 wt % of the optical sulfur
copolymer.
In one embodiment, the optical sulfur copolymer may comprise about
50 wt % sulfur monomers, about 15 wt % comonomers, and about 35 wt
% selenium. For example, the sulfur copolymer may comprise sulfur,
DIB and selenium (Se). The sulfur copolymer may have a refractive
index of about n=2.01. Typically, Se has a refractive index
n.about.2.6-2.7 in IR regime. Without wishing to limit the present
invention to a particular theory or mechanism, by adding Se to the
inverse vulcanization process, it can enable a dramatic increase in
refractive index, as measured using ellipsometric characterization
methods across the wavelength regime from 500-1500 nm.
In one embodiment, the optical sulfur copolymer may further
comprise one or more epoxide monomers at a level in the range of
about 10 wt % to about 50 wt % of the optical sulfur copolymer. At
least one epoxy functional moiety of the epoxide monomers may be
bonded to a functional moiety of the sulfur copolymer. Preferably,
when one or more S--S bonds of the sulfur copolymer are broken, the
S--S bonds are reconnected by thermal reforming.
In another embodiment, the optical sulfur copolymer may further
comprise one or more termonomers selected from amine monomers,
thiol monomers, sulfide monomers, alkynylly unsaturated monomers,
epoxide monomers, nitrone monomers, aldehyde monomers, ketone
monomers, thiirane monomers, and ethylenically unsaturated monomers
at a level in the range of about 10 wt % to about 50 wt % of the
optical sulfur copolymer.
In further embodiments, the optical sulfur copolymer may further
comprise one or more polyfunctional monomers selected from a
polyvinyl monomer, a polyisopropenyl monomer, a polyacryl monomer,
a polymethacryl monomer, a polyunsaturated hydrocarbon monomer, a
polyepoxide monomer, a polythiirane monomer, a polyalkynyl monomer,
a polydiene monomer, a polybutadiene monomer, a polyisoprene
monomer, a polynorbornene monomer, a polyamine monomer, a polythiol
monomer, a polysulfide monomer, a polyalkynylly unsaturated
monomers, a polynitrone monomers, a polyaldehyde monomers, a
polyketone monomers, and a polyethylenically unsaturated
monomers.
In some embodiments, the optical sulfur copolymer is substantially
transparent in an infrared or visible spectrum. For example, the
optical sulfur copolymer can be substantially transparent in an
electromagnetic spectrum having a wavelength range of about
1000-1500 nm, or about 3000-5000 nm, or about 5-10 microns. In
other embodiments, the selenium of the optical sulfur copolymer may
have a refractive index of about 2.6-2.7 in the infrared spectrum.
In further embodiments, the optical sulfur copolymer is formed into
a substantially transparent substrate, such as a film, a lens, or a
free-standing object.
Another embodiment of the present invention features a method of
producing a sulfur copolymer. The method may comprise providing
elemental sulfur, heating the elemental sulfur to a temperature of
about 120-130.degree. C. to form a molten sulfur, and polymerizing
one or more comonomers with the molten sulfur to form the sulfur
copolymer. The one or more monomers may be selected from amine
monomers, thiol monomers, sulfide monomers, alkynylly unsaturated
monomers, epoxide monomers, nitrone monomers, aldehyde monomers,
ketone monomers, thiirane monomers, and ethylenically unsaturated
monomers. Preferably, the amount of elemental sulfur is at least
500 g. In some embodiments, the technique of polymerizing is free
radical polymerization, controlled radical polymerization,
ring-opening polymerization, ring-opening metathesis
polymerization, step-growth polymerization, or chain-growth
polymerization.
The present invention may also feature a method of producing an
optical sulfur copolymer comprising providing elemental sulfur,
heating the elemental sulfur to form a molten sulfur, mixing one or
more comonomers with the molten sulfur, and heating the optical
sulfur copolymer for a period of time to sufficiently vitrify the
optical sulfur copolymer. In an alternate embodiment, the method of
producing an optical sulfur copolymer may comprise providing about
5-95 wt % elemental sulfur, heating the elemental sulfur to form a
molten sulfur, mixing about 10-90 wt % selenium monomers with the
molten sulfur to form a sulfur-selenium mixture, mixing about 1-50
wt % one or more comonomers with the sulfur-selenium mixture such
that the one or more comonomers polymerizes with the molten sulfur
to form the optical sulfur copolymer, and heating the optical
sulfur copolymer for a period of time, such as 5 to 15 minutes, to
sufficiently vitrify the optical sulfur copolymer.
In some embodiments, the one or more monomers is selected amine
monomers, thiol monomers, sulfide monomers, alkynylly unsaturated
monomers, epoxide monomers, nitrone monomers, aldehyde monomers,
ketone monomers, thiirane monomers, and ethylenically unsaturated
monomers, wherein the one or more comonomers polymerizes with the
molten sulfur to form the optical sulfur copolymer. In other
embodiments, the selenium comonomers are derived from cyclic
selenium sulphide, elemental selenium, or a combination thereof. In
further embodiments, the technique of polymerizing is free radical
polymerization, controlled radical polymerization, ring-opening
polymerization, ring-opening metathesis polymerization, step-growth
polymerization, or chain-growth polymerization.
As shown in FIG. 24-26, the sulfur copolymers that have been
described herein are the first class of polymeric materials that
exhibit high transparency in the short-wave and mid-IR regimes due
to the presence of largely IR inactive S--S bonds. Furthermore,
since these sulfur copolymers are readily melt, or solution
processed, fabrication of free standing films, windows, or lenses
can be easily conducted. Access to these kinds of high quality and
inexpensive lenses are anticipated to open new opportunities in low
cost IR optical devices and technologies including IR thermal
imaging rifle scopes and home monitoring.
As shown in FIGS. 33-34, the refractive index of poly(S-r-DIB) film
is >22% higher than PMMA, and the transparency of poly(S-r-DIB)
film is 6.times. higher at 2900 nm. Sulfur-rich copolymers were
synthesized via inverse vulcanization to create novel copolymers
with high refractive indices and optical transparency in the near
to mid-infrared (1.5 um and 3-5 um) regions. By directly varying
the feed ratio of comonomers during inverse vulcanization, the
content of S--S bonds in these materials was controlled, thereby
enabling correlation of optical properties with copolymer
composition. All copolymer compositions possess a refractive index
above n=1.7 at 1550 nm. Furthermore, these sulfur copolymers were
readily solution, or melt processed into thin films, or free
standing lenses for IR imaging.
Another feature of the present invention teaches the synthesis of
an optical sulfur copolymer via the copolymerization of elemental
sulfur with comonomers. The optical sulfur copolymer comprises
monomers of sulfur and comonomers of ethylenically unsaturated
monomers (e.g., vinylic, divinylic, multi-vinylic comonomers,
substituted alkenes, and functional alkenes), alkynylly unsaturated
monomer (e.g., alkynes, dialkynes, and multi-alkynes), amine
monomers (e.g., amines, diamines, and multi-amines), thiol monomer
(e.g., thiols, dithiols, multi-functional thiols), nitrone and
nitroso monomers (e.g., nitrones, dinitrones, and multi-nitrones),
aldehyde monomers (e.g., aldehydes, dialdehydes, and
multi-aldehydes), ketone monomers, thiirane monomers, or epoxide
monomers.
For example, new types of optical sulfur copolymer were prepared by
the copolymerization of elemental sulfur with vinylic compounds
carrying thiophene, or amine, or pyrrole side chain groups, where
subsequent oxidative or electrochemical polymerization affords the
new copolymer material. Vinylic monomers, utilizing groups, such
as, styrenics, incorporating thiophene groups, such as,
3,4-alkylenedioxythiophenes and 3,4-propylenedioxythiophenes
(ProDOT) are examples of these functional monomers. As another
example, new optical sulfur copolymer are also demonstrated by the
copolymerization of elemental sulfur with amines e.g.,
phenylenediamines that can be oxidatively copolymerized with
aniline to prepare polyaniline-sulfur copolymer materials.
In an alternative embodiment, a new polymeric material is prepared
by post-modification of the amine, thiol, or other functional
groups of the optical sulfur copolymer to either modify the
chemical functionality of the copolymer, crosslink the copolymer,
or form other new copolymers, such as polyethers via epoxide
copolymerizations, polyurethanes and polyamides.
In another embodiment, the optical sulfur copolymer is prepared via
distinct synthesis and post-functionalization methods to introduce
conjugated polymers, such as, polythiophenes, polyanilines, or
polypyrroles. Methods include, but are not limited to, the
copolymerization of a vinylic comonomer carrying a pendant
thiophene that forms the polythiophene phase after an oxidative, or
electrochemical polymerization. Other methods include
copolymerization of sulfur with diamines that carry free reactive
amines that can copolymerize with monomers, such as, aniline, and
then oxidative or electrochemical polymerization to form the
polyaniline phase.
In some embodiments, the optical sulfur copolymer comprises one or
more sulfur monomers at a level in the range of about 5 to about 99
wt % of the optical sulfur copolymer, and one or more monomers at a
level in the range of about 1 wt % to about 95 wt % of the optical
sulfur copolymer. In another embodiment, the sulfur copolymer
comprises one or more sulfur monomers at a level in the range of
about 50 to about 97.5 wt % of the sulfur copolymer, and one or
more monomers at a level in the range of about 2.5 wt % to about 50
wt % of the sulfur copolymer, or one or more sulfur monomers at a
level in the range of about 50 to about 95 wt % of the sulfur
copolymer, and one or more monomers at a level in the range of
about 5 wt % to about 50 wt % of the sulfur copolymer.
In some embodiments, the optical sulfur copolymer comprises one or
more sulfur monomers at a level of at least about 5 wt % of the
optical sulfur copolymer. The sulfur copolymer may comprise one or
more sulfur monomers at a level of at least about 10 wt %, or at
least about 20 wt %, or at least about 30 wt %, or at least about
40 wt %, or at least about 50 wt %, or at least about 60 wt %, or
at least about 70 wt %, or at least about 80 wt %, or at least
about 90 wt % of the sulfur copolymer.
In other embodiments, the optical sulfur copolymer comprises one or
more sulfur monomers at a level in the range of about 5 to about 10
wt % of the optical sulfur copolymer. The sulfur copolymer may
comprise one or more sulfur monomers at a level in the range of
about 10 to 20 wt %, or in the range of about 20 to 30 wt %, or in
the range of about 30 to 40 wt %, or in the range of about 40 to 50
wt %, or in the range of about 50 to 60 wt %, or in the range of
about 60 to 70 wt %, or in the range of about 70 to 80 wt %, or in
the range of about 80 to 90 wt %, or in the range of about 90 to 95
wt % of the sulfur copolymer.
In some embodiments, the optical sulfur copolymer comprises one or
more comonomers at a level of at least 0.1 wt % of the optical
sulfur copolymer, or at least about 0.5 wt %, or at least about 1
wt %, or at least about 5 wt %, or at least about 10 wt %, or at
least about 20 wt %, or at least about 30 wt %, or at least about
40 wt %, or at least about 50 wt %, or at least about 60 wt %, or
at least about 70 wt %, or at least about 80 wt %, or at least
about 90 wt %, or at least about 95 wt % of the sulfur
copolymer.
In other embodiments, the optical sulfur copolymer comprises one or
more comonomers at a level in the range of about 5 to about 10 wt %
of the optical sulfur copolymer. The sulfur copolymer may comprise
one or more comonomers at a level in the range of about 10 to 20 wt
%, or in the range of about 20 to 30 wt %, or in the range of about
30 to 40 wt %, or in the range of about 40 to 50 wt %, or in the
range of about 50 to 60 wt %, or in the range of about 60 to 70 wt
%, or in the range of about 70 to 80 wt %, or in the range of about
80 to 90 wt %, or in the range of about 90 to 95 wt % of the sulfur
copolymer.
In a further embodiment, the optical sulfur copolymer comprises one
or more selenium comonomers at a level in the range of about 5 wt %
to 10 wt % of the optical sulfur copolymer. The sulfur copolymer
may comprise one or more selenium comonomers at a level in the
range of about 10 to 20 wt %, or in the range of about 20 to 30 wt
%, or in the range of about 30 to 40 wt %, or in the range of about
40 to 50 wt %, or in the range of about 50 to 60 wt %, or in the
range of about 60 to 70 wt %, or in the range of about 70 to 80 wt
%, or in the range of about 80 to 90 wt % of the optical sulfur
copolymer.
In some embodiments, the present invention features a method for
making any of the aforementioned optical sulfur copolymers. The
method comprises heating a mixture comprising sulfur and one or
more monomers at a temperature in the range of about 120.degree. C.
to about 230.degree. C., and allowing for polymerization of the
mixture. For example, the mixture may be heated to a temperature
between about 120.degree. C. to 130.degree. C., or about
130.degree. C. to 140.degree. C., or about 140.degree. C. to
150.degree. C., or about 150.degree. C. to 160.degree. C., or about
160.degree. C. to 170.degree. C., or about 170.degree. C. to
180.degree. C., or about 180.degree. C. to 190.degree. C., or about
190.degree. C. to 200.degree. C., or about 200.degree. C. to
210.degree. C., or about 210.degree. C. to 220.degree. C., or about
220.degree. C. to 230.degree. C.
In other embodiments, an article is made from any of the
aforementioned optical sulfur copolymer. For instance, the method
of forming the article may comprise heating a mixture comprising
sulfur and one or more monomers at a temperature in the range of
about 160.degree. C. to about 230.degree. C. to form a prepolymer,
forming the prepolymer into the shape of the article, to yield a
formed prepolymer shape, and heating the formed prepolymer shape to
yield the article.
In another embodiment, a method of forming the article comprises
admixing the optical sulfur copolymer in a nonpolar organic
solvent, forming the admixed optical sulfur copolymer into the
shape of the article, and removing the solvent from the optical
sulfur copolymer to yield the article. In some embodiments, the
optical sulfur copolymer is provided as a mixture with a solvent
for forming. In other embodiments, the optical sulfur copolymer is
coated and cured as a thin film on a substrate. In still other
embodiments, the optical sulfur copolymer is shaped and cured using
a mold.
In some embodiments, any of the optical sulfur copolymers can be
modified by reacting an available reactive functional group on the
polymeric composition with a second comonomer to form a new
copolymer material. The technique of reacting may be oxidative
coupling, polymerization, or copolymerization. In some embodiments,
the reactive functional group is an amine or a thiol. The second
comonomer may comprise an epoxide, isocyanate, acid chloride,
carboxylic acid, ester, or alkyl halide group. In some embodiments,
when the reactive functional group is an amine, the new copolymer
material is a polyurethane or a polyamide. In some embodiments,
when the reactive functional group is an aniline or a
phenylenediamine, and the new copolymer material contains oligo- or
polyaniline segments. In some embodiments, the reactive functional
group is a thiophene and the new copolymer material contains oligo-
or polythiophene segments.
According to some embodiments, the present invention features a
method of making an optical substrate. The method may comprise
heating any of the copolymers described herein to a temperature in
the range of about 160-230.degree. C.; and forming the copolymer
into a shape of the optical substrate. Preferably, the optical
substrate has a refractive index of about 1.7-2.6 at a wavelength
in a range of about 500 nm to about 8 .mu.m, and can be
substantially transparent in an infrared or visible spectrum. The
optical substrate may an optical device component, such as a lens
or window, for use as a transmitting material in an infrared
imaging device.
According to other embodiments, the present invention features a
method of preparing an optical thin-film polymer. The method may
comprise providing any of the copolymers described herein in a form
of a powder; placing the copolymer between two plates; heating the
plates and the copolymer to a first temperature; applying a first
pressure to the two plates to compress the copolymer for a first
allotted time to form the optical thin-film polymer; applying a
second pressure to the two plates to compress the optical thin-film
polymer for a second allotted time, wherein the second pressure is
greater than the first pressure; and cooling the optical thin-film
polymer. Preferably, the optical thin-film polymer has a refractive
index of about 1.7-2.6 at a wavelength in a range of about 500 nm
to about 8 .mu.m, and can be substantially transparent in an
infrared or visible spectrum. The optical thin-film polymer may be
used as a transmitting material in an infrared imaging device.
According to further embodiments, the present invention features a
method of preparing an optical polymer lens. The method may
comprise preparing a lens mold; providing any of the copolymers
described herein; pouring the copolymer into the lens mold to form
a molded copolymer; curing the molded copolymer to vitrify the
molded copolymer into the optical polymer lens; and removing the
optical polymer lens from the lens mold. Preferably, the optical
polymer lens has a refractive index of about 1.7-2.6 at a
wavelength in a range of about 500 nm to about 8 .mu.m, and can be
substantially transparent in an infrared or visible spectrum. The
optical polymer lens can be used as a transmitting material in an
infrared imaging device.
In exemplary embodiments, the step of preparing the lens mold may
comprise mixing an elastomeric base with a curing agent to form a
replica mixture; pouring the replica mixture over a master lens to
form the lens mold; placing the lens mold under reduced pressure to
remove bubbles in the lens mold; curing the lens mold; and removing
the lens mold from the master lens.
In further embodiments, the present invention features a method of
depositing a copolymer onto a substrate. The method may comprise
providing any of the copolymers described herein; heating the
substrate; and coating the heated substrate with the copolymer. The
method may further comprise curing the heated substrate coated with
the copolymer. Preferably, the copolymer has a refractive index of
about 1.7-2.6 at a wavelength in a range of about 500 nm to about 8
.mu.m, and is substantially transparent in an infrared or visible
spectrum. The copolymer-coated substrate can be used as a
transmitting material in an infrared imaging device.
In an exemplary embodiment, the step of coating the heated
substrate with the copolymer comprises spin-coating the copolymer
onto the heated substrate. In one embodiment, the process of
spin-coating may comprise spinning the heated substrate at a first
rotational speed with a first acceleration for a first time period
while simultaneously disposing the copolymer on the heated
substrate to coat the heated substrate with the copolymer; and
spinning the heated substrate coated with the copolymer at a second
rotational speed with a second acceleration for a second time
period. Preferably, the first rotational speed is less than the
second rotational speed. Alternatively, the first rotational speed
is greater than the second rotational speed In one embodiment, the
first time period or second time period is about 10 to 30 seconds.
For instance, the first time period is about 20 seconds, and the
second time period is about 10 seconds.
In some embodiments, the copolymers described herein are provided
as a mixture with a solvent for forming. In other embodiments, the
copolymer is coated and cured as a thin film on a substrate. In
still other embodiments, the copolymer is shaped and cured using a
mold.
In some embodiments, any of the copolymers can be modified by
reacting an available reactive functional group on the polymeric
composition with a second comonomer to form a new copolymer
material. The technique of reacting may be oxidative coupling,
polymerization, or copolymerization.
In some embodiments, the copolymer is a thermoset. In some
embodiments, the copolymer is a thermoplastic. In some embodiments,
the copolymer is self-healing. In some embodiments, when one or
more S--S bonds of the copolymer are broken, the S--S bonds are
reconnected by thermal reforming.
In some embodiments, the present invention features a method of
repairing an optical substrate, said method comprising providing
the optical substrate comprising any of the copolymers described
herein, the copolymer having one or more broken S--S bonds, and
heat treating the optical substrate at a healing temperature for a
period of time in order to reconnect the S--S bonds of the
copolymer. In some embodiments, the healing temperature is between
about 80.degree. C. and 100.degree. C. In some embodiments, the
healing temperature is between about 100.degree. C. and 150.degree.
C. In some embodiments, the healing temperature is at or near the
melting point of the polymeric substrate. In some embodiments, the
period of time is between about 4 and 15 hours. In some
embodiments, the period of time is between about 8 and 12
hours.
Example 13. Thermal Reforming Procedure of a Self-Healing Optical
Substrate
1. The optical substrate having a crack is placed in an oven.
2. The optical substrate is heated at a temperature of about
100.degree. C. for about 3 hours.
3. The optical substrate is inspected to ensure that it is
completely self-healed.
Because both anionic and radical polymerization can occur in the
polymerization reaction mixtures, any desirable combination of
amine comonomers, thiol comonomers, sulfide comonomers, alkynylly
unsaturated comonomers, epoxide comonomers, nitrone comonomers,
aldehyde comonomers, ketone comonomers, thiirane comonomers,
ethylenically unsaturated comonomers, styrenic comonomers, vinylic
comonomers, methacrylate comonomers, and acrylonitrile comonomers
can be used in the same copolymer. As non-limiting examples, in one
embodiment of the invention, the one or more monomers are a
combination of one or more amine monomers and one or more styrenic
monomers.
In preferred embodiments, any of the sulfur polymers described
herein can be melt processable or processable in a solution. The
sulfur polymer can also be self-healing upon thermal reprocessing.
For example, the sulfur monomers comprise dynamic sulfur-sulfur
(S--S) bonds that when broken can be reconnected by thermal
reforming.
A person of skill in the art will select activators monomers and
relative ratios thereof in order to provide the desired properties
to the polymer. In certain embodiments, the one or more monomers
include one or more polyfunctional monomers, optionally in
combination with one or more monofunctional monomers. A
polyfunctional monomer is one that includes more than one (e.g., 2,
or 3) polymerizable amine, thiol, sulfide, alkynylly unsaturated,
nitrone and/or nitroso, aldehyde, ketone, thiirane, ethylenically
unsaturated, and/or epoxide moieties. Polyfunctional monomers can
be used to cross-link the sulfur or sulfur polymer chains to adjust
the properties of the polymer, as would be understood by the person
of skill in the art. The multiple polymerizable groups of a
polyfunctional monomer can be the same or different.
Frechet-type benzyl ether dendrimers bearing styrenic terminal
groups are miscible with liquid sulfur and can be used as
polyfunctional cross-linkers. In certain embodiments, the one or
more polyfunctional monomers include one or more of a
divinylbenzene, a diisopropenylbenzene, an alkylene
di(meth)acrylate, a bisphenol A di(meth)acrylate, a terpene, a
carotene, a divinyl (hetero)aromatic compound, and a diisopropenyl
(hetero)aromatic compound. In other embodiments, a polyfunctional
monomer can have one or more amine, thiol, sulfide, alkynylly
unsaturated, nitrone and/or nitroso, aldehyde, ketone, thiirane,
ethylenically unsaturated, and/or epoxide moieties moieties; and
one or more amine, thiol, sulfide, alkynylly unsaturated, nitrone
and/or nitroso, aldehyde, ketone, thiirane, ethylenically
unsaturated, and/or epoxide moieties, wherein the first and second
moieties are different. A non-limiting example is a divinylbenzene
monoxide.
Embodiments of the present invention featuring any of sulfur
polymers described herein may further comprise an elemental carbon
material, which may be dispersed in the sulfur polymer, in an
amount of at most about 50 wt % of the sulfur polymer. In some
embodiments, the methods of synthesizing any of the sulfur polymers
described herein may further comprise the step of dispersing an
elemental carbon material in the sulfur copolymers. For example,
the carbon material is at most about 5 wt %, or at most about 10 wt
%, or at most about 20 wt %, or at most about 30 wt %, or at most
about 40 wt %, or at most about 50 wt % of the sulfur polymer.
The sulfur polymers can be made, for example, by polymerization of
a molten mixture of sulfur with the non-homopolymerizing monomers.
Thus, in one aspect, the invention provides a method for making
sulfur polymers as described above. The method includes heating a
mixture of elemental sulfur or sulfur comonomers and the
non-homopolymerizing monomers together at a temperature sufficient
to initiate polymerization (i.e., through free radical
polymerization, through anionic polymerization, or through both,
depending on the monomers used). For example, in one embodiment,
the method includes heating the mixture to a temperature in the
range of about 120.degree. C. to about 230.degree. C., e.g., in the
range of about of about 120.degree. C. to about 170.degree. C. or
about 170.degree. C. to about 230.degree. C. The person of skill in
the art will select conditions that provide the desired level of
polymerization, In certain embodiments, the polymerization reaction
is performed under ambient pressure. However, in other embodiments,
the polymerization reaction can be performed at elevated pressure
(e.g., in a bomb or an autoclave). Elevated pressures can be used
to polymerize more volatile monomers, so that they do not vaporize
under the elevated temperature reaction conditions.
In certain embodiments, it can be desirable to use a nucleophilic
viscosity modifier in liquefying the elemental sulfur or sulfur
comonomers, for example, before adding the non-homopolymerizing
monomers. For example, in certain embodiments, the elemental sulfur
or sulfur comonomers is first heated with a viscosity modifier,
then the viscosity-modified elemental sulfur or sulfur comonomers
is heated with the non-homopolymerizing monomers. The nucleophilic
viscosity modifier can be, for example, a phosphorus nucleophile
(e.g., a phosphine), a sulfur nucleophile (e.g., a thiol) or an
amine nucleophile (e.g., a primary or secondary amine). When the
elemental sulfur or sulfur comonomers is heated in the absence of a
nucleophilic viscosity modifier, the elemental sulfur or sulfur
comonomers rings can open to form, e.g., diradicals, which can
combine to form linear polymer chains which can provide a
relatively high overall viscosity to the molten material.
Nucleophilic viscosity modifiers can break these linear chains into
shorter lengths, thereby making shorter polymers that lower the
overall viscosity of the molten material, making the elemental
sulfur or sulfur comonomers mixture easier to mix with and other
species, and easier to stir for efficient processing. Some of the
nucleophilic viscosity modifier will react to be retained as a
covalently bound part of the polymer, and some will react to form
separate molecular species, with the relative amounts depending on
nucleophile identity and reaction conditions. While some of the
nucleophilic viscosity modifier may end up as a separate molecular
species from the polymer chain, as used herein, nucleophilic
viscosity modifiers may become part of the polymer. Non-limiting
examples of nucleophilic viscosity modifiers include
triphenylphosphine, aniline, benzenethiol, and
N,N-dimethylaminopyridine. Nucleophilic viscosity modifiers can be
used, for example, in an amount up to about 10 wt %, or even up to
about 5 wt % of the sulfur polymer. When a nucleophilic viscosity
modifier is used, in certain embodiments it can be used in the
range of about 5 wt % to about 15 wt % of the sulfur polymer.
In certain embodiments, a monofunctional monomer can be used to
reduce the viscosity of the sulfur polymer, for example, before
adding other monomers (e.g., before adding any polyfunctional
monomer). For example, in certain embodiments, the elemental sulfur
or sulfur copolymers is first heated with one or more
monofunctional monomers. While not intending to be bound by theory,
the inventors surmise that inclusion of monofunctional monomers
into the poly(sulfur) chains disrupts intermolecular associations
of the elemental sulfur or sulfur copolymers, and thus decreases
the viscosity. The monofunctional monomer can be, for example, a
mono(meth)acrylate such as benzyl methacrylate, a mono(oxirane)
such as a styrene oxide or a glycidyl phenyl ether, or a
mono(thiirane) such as t-butyl thiirane or phenoxymethylthiirane. A
monofunctional monomer can be used to modify the viscosity of the
sulfur polymer, for example, in an amount up to about 10 wt %, up
to about 5 wt %, or even up to about 2 wt % of the copolymer. When
a monofunctional monomer can be used to modify the viscosity of the
sulfur polymer, in certain embodiments it can be used in the range
of about 0.5 wt % to about 5 wt %, or even about 0.5 wt % to about
3 wt % of the sulfur polymer.
Of course, viscosity modification is not required, so in other
embodiments the elemental sulfur or sulfur copolymers are heated
together with the non-homopolymerizing monomers (and particularly
with one or more polyfunctional monomers) without viscosity
modification. In other embodiments, a solvent, e.g., a halobenzene
such as 1,2,4-trichlorobenzene, a benzyl ether, or a phenyl ether,
can be used to modify the viscosity of the materials for ease of
handling. The solvent can be added, for example, to the elemental
sulfur or sulfur copolymers before reaction with a monomer in order
to reduce its viscosity, or to the polymerized material in order to
aid in processing into a desired form factor.
The polymers described herein can be partially cured to provide a
more easily processable material, which can be processed into a
desired form (e.g., into a desired shape, such as in the form of a
free-standing shape or a device), then fully cured in a later
operation. For example, one embodiment of the invention is a method
of making an article formed from the sulfur polymers as described
herein. The method includes heating the sulfur polymer at a
temperature in the range of about 120.degree. C. to about
220.degree. C. (e.g. 120.degree. C. to about 150.degree. C.) to
form a prepolymer; forming the prepolymer into the shape of the
article, to yield a formed prepolymer shape; and further heating
the formed prepolymer shape to yield the article. The prepolymer
can be formed, for example, by conversion of the one or more
monomers at a level in the range of about 20 to about 50 mol %. For
example, heating the sulfur polymer to form the prepolymer can be
performed for a time in the range of about 20 seconds to about five
minutes, for example, at a temperature in the range of about
175.degree. C. to about 195.degree. C. In one embodiment, the
heating is performed for less than about 2 minutes at about
185.degree. C. The person of skill in the art will determine the
desired level of monomer conversion in the prepolymer stage to
yield a processable prepolymer material, and will determine process
conditions that can result in the desired level of monomer
conversion.
In one embodiment, the prepolymer can be provided as a mixture with
a solvent for forming, e.g., via casting, molding or printing. The
prepolymers described herein can form miscible mixtures or
solutions with a variety of nonpolar high-boiling aromatic
solvents, including, for example, haloarene solvents such as di-
and trichlorobenzene (e.g., 1,2,4-trichlorobenzene). The solvent
can be added, for example, after the prepolymer is prepared, to
provide a softened or flowable material suitable for a desired
forming step (e.g., casting, molding, or spin-, dip- or
spray-coating.) In some embodiments, the prepolymer/solvent mixture
can be used at elevated temperatures (e.g., above about 100.degree.
C., above about 120.degree. C. or above about 140.degree. C.) to
improve flow at relatively low solvent levels (e.g., for use in
casting or molding processes). In other embodiments, the
prepolymer/solvent mixture can be used at a lower temperature, for
example, at ambient temperatures. The prepolymers described herein
can remain soluble even after the solvent cools.
In one embodiment, the prepolymer can be provided as a mixture with
a solvent for forming, e.g., via casting, molding or printing. The
prepolymers described herein can form miscible mixtures or
solutions with a variety of solvents, such as non-polar
high-boiling aromatic solvents, including, for example, haloarene
solvents such as di- and trichlorobenzene (e.g.,
1,2,4-trichlorobenzene). The solvent can be added, for example,
after the prepolymer is prepared, to provide a softened or flowable
material suitable for a desired forming step (e.g., casting,
molding, or spin-, dip- or spray-coating.) In some embodiments, the
prepolymer/solvent mixture can be used at elevated temperatures
(e.g., above about 100.degree. C., above about 120.degree. C. or
above about 140.degree. C.) to improve flow at relatively low
solvent levels (e.g., for use in casting or molding processes). In
other embodiments, the prepolymer/solvent mixture can be used at a
lower temperature, for example, at ambient temperatures (e.g., for
use in spin-coating processes). Unlike molten sulfur, the
prepolymers described herein can remain soluble even after the
solvent cools.
In one embodiment, the prepolymer is coated and cured as a film on
a substrate. While S.sub.8 is typically intractable due to its
crystallinity, the materials described herein can be formed as to
be amenable to solution processing (e.g., in molten or
solvent-admixed form) to fabricate thin film materials. Mixtures of
molten prepolymer and solvent can be diluted to the concentration
desired for a given spin-coating process.
When forming thin films of the materials described herein on
substrates, it can often be desirable to use a polyimide primer
layer. Thus, a solution of a polyamic precursor (e.g.,
polypyromellitamic acid-4,4'-dianiline, or compounds with
oxyaniline linkages), or similar copolymer derivatives can be
deposited onto a substrate and cured (e.g., by heating at a
temperature in the range of about 120 to about 220.degree. C.) to
form a thin polyimide layer (e.g., as thin as 2 nm), upon which the
materials described herein can be formed. Moreover, in many
embodiments, even fully cured polymers as described herein can be
melt processed or suspended or dissolved in solvent and deposited
on to substrates in a manner similar to those described for
prepolymeric materials.
In certain embodiments, the prepolymer can be shaped and cured
using a mold. For example, in one embodiment, the prepolymer (i.e.,
in liquid or solvent-admixed form) can be deposited (e.g., by
pouring) into a TEFLON or silicone (e.g., polydimethylsiloxane
(PDMS)) mold, then cured to form a desired shape. In another
embodiment, a softened prepolymer material (e.g., swollen with
solvent and/or softened by heat) can be imprinted by stamping with
a mold bearing the desired inverse surface relief, then cured and
allowed to cool. Moreover, in many embodiments, even fully cured
copolymers as described herein can be shaped with a mold in a
manner similar to those described for prepolymeric materials.
Sulfur terpolymers and more complex copolymer materials, such as in
the form of cross-linked polymers, or non-crosslinked, intractable
polymers, can be reprocessed by thermal or other stimuli activation
of dynamic S--S bonds in the polymer system.
As described above, soluble sulfur polymers can be made by the
person of skill in the art, for example, using relatively higher
fractions of organic monomer(s). Such polymers can be solution
processed to fabricate articles. For example, another aspect of the
invention is a method of forming an article formed from a sulfur
polymer as described herein, the method comprising admixing the
sulfur polymer with a nonpolar organic solvent (e.g., to make a
suspension or solution), forming the admixed sulfur polymer into
the shape of the article, and removing the solvent from the sulfur
polymer to yield the article. The admixture with solvent can, for
example, dissolve the sulfur polymer. Various process steps can be
performed at elevated temperatures, for example, to decrease
viscosity of the admixed sulfur polymer and to aid in evaporation
of solvent.
For example, in one embodiment, a room temperature solution of any
sulfur polymer described herein (e.g., in prepolymeric form) is
poured into a TEFLON or PDMS mold. A decrease in viscosity at
elevated temperatures (e.g., > about 140.degree. C.) can allow
sufficient flow into even intricate mold shapes. Once the mold is
filled, it can be placed in a vacuum oven at increased temperature
(e.g., about 210.degree. C.) under ambient pressure to cure and to
drive off solvent. For thicker molded samples, vacuum can be pulled
on the solution when it is in a low viscosity state in order to
ensure the removal of bubbles. The mold is then removed from the
oven and allowed to cool before removal from the mold.
As the polymeric materials described herein can be effectively
thermoplastic in nature, the person of skill in the art will
understand that other methods familiar in the thermoplastic
industries, such as injection molding, compression molding, and
melt casting, can be used in forming articles from the materials
described herein.
The chemistry via the copolymerization of the one or more monomers
of amine monomers, thiol monomers, sulfide monomers, alkynylly
unsaturated monomers, nitrone monomers, aldehyde monomers, and
ketone monomers in liquid as used herein produce these advantageous
sulfur copolymer compositions. For example, the amine monomer, such
as those on aromatic compounds, results in direct C--S bond
formation and copolymerization with sulfur concurrently. Thiol
monomers from a wide range of comonomer precursors widely used in
the preparation of condensation polymers can be dissolved and
copolymerization with liquid sulfur to afford high sulfur content
copolymers. Unexpectedly, the thiol derived copolymer was solution
processable despite the high content of sulfur and rigid aromatic
moieties. Sulfide monomers can copolymerize with sulfur via either
ionic, or free radical processes. Unexpectedly, the sulfide monomer
was able to afford both low glass transition polymers, or higher
glass transition polymers. As another example, the alkynylly
unsaturated monomer is expected to react via known thiol-yne
processes, however, unexpectedly, the alkynylly unsaturated monomer
was able to afford polythiophene and other heterocycles. The
nitrone monomer is expected to react via free radical
polymerizations with sulfur radicals. Unexpectedly, the nitrone
monomer was designed to afford polymeric materials when
copolymerized with elemental sulfur. Aldehyde based monomers are
not expected to react with sulfur radicals, however, the formation
of polymers was observed when the appropriate di-, or
multifunctional aldehydes are copolymerized with sulfur. Ketone
based monomers are not expected to react with sulfur radicals,
however, the formation of polymers was observed when the
appropriate di-, or multifunctional ketones are copolymerized with
sulfur.
As used herein, the term "about" refers to plus or minus 10% of the
referenced number.
Various modifications of the invention, in addition to those
described herein, will be apparent to those skilled in the art from
the foregoing description. Such modifications are also intended to
fall within the scope of the appended claims. Each reference cited
in the present application is incorporated herein by reference in
its entirety.
Although there has been shown and described the preferred
embodiment of the present invention, it will be readily apparent to
those skilled in the art that modifications may be made thereto
which do not exceed the scope of the appended claims. Therefore,
the scope of the invention is only to be limited by the following
claims. In some embodiments, the figures presented in this patent
application are drawn to scale, including the angles, ratios of
dimensions, etc. In some embodiments, the figures are
representative only and the claims are not limited by the
dimensions of the figures. In some embodiments, descriptions of the
inventions described herein using the phrase "comprising" includes
embodiments that could be described as "consisting of", and as such
the written description requirement for claiming one or more
embodiments of the present invention using the phrase "consisting
of" is met.
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